First a person who only wants to record a single mic forever is an animal that rarely exists.
Well they do; they are called rappers or fellows who sing over electronica where the vocal may be the only acoustic track. These fellows are traditionally given either rude treatment or bad advice here, and I am *really* tired of it.
The second class is those who will be happy with stereo recording, and that's quite a lot of hobbyists. USB mic design does need to change to accommodate them.
When they start out, they can rarely see that they will want to expand their horizons in the future but most do (or else give up and leave the USB mic to gather dust anyway). I believe the best advice is to suggest the building blocks of a system that can be expanded upon without total replacement in the future.
I counter that it's a mic that will always have a use, especially if they can toss it in their pocket and use it with their tablet.
Second, the "simplicity" of USB mics (I'll call them that since, at the economy end of the market, that's what they're know as) is over-rated and often untrue. Yes, you have one cable to plug in and no knobs to twiddle but just look at how many questions relating to the DAW side of things are caused by the flakey (or at least non specialist) nature of the drivers being use.
With respect to USB AC I don't agree, that is supported natively in nearly all computers and many portable devices. I have seen a much higher rate of driver difficulties over the years with Firewire interfaces, for example. I've never had a problem with a USB AC device; a USB device with its own flaky drivers, sure I believe that, but USB interfaces would potentially have the same difficulties. Again, if the physical circuit components are the same--which they largely are--why would there be a difference?
Third, as hinted at above, for anything beyond the most basic home recording, you need some form of external sound card anyway simply for the output side of things. Yes, there are a few mics that also provide headphone outputs but they're the exception, not the rule--and once people follow advice and buy proper monitor speakers, what then?
You can drive active monitors from a headphone out. Yes, all USB mics should have an out unless they are special-purpose mics where that is not important.
Fourth, the maximum cable length allowed within the USB2 spec is 5 metres. In all but the simplest of set ups, this is going to force compromises in terms of the relative positions of mic and computer. Again, a common theme of advice given on this forum is to be aware of the effect mic placement and room acoustics have on recording.
I almost never use a cable longer than 5m in my studio, and I have a room larger than the average bedroom. I did have the foresight to wire three of my walls with multicore, which nobody is ever going to do in the future; that limits my need for long cables. One solution for extension is a hub, then you get to 10m which is plenty for 90% of home use. The other elephant-in-the-room solution is the inline USB adaptors, that gets around your single-kind-of-mic objection and allows traditional analog extension. Those aren't quite as elegant from a design point of view, but they are more flexible.
Also, when you are recording to a portable device--which will very quickly become the preference--then you don't want the tablet far away from you anyway. They don't have fans, so they don't make noise . . .
The trend is going to be towards going to better rooms/halls/etc. to record with your USB mic and your tablet, and then *maybe* returning to the home studio for postproduction. I mean I always used to stick with the standard advice not to mix on headphones, but a lot of young musicians (and especially their fans) don't even own speakers. Plus, DSP algos are good enough to do a better mix than 90% of hobbyists. Sad but true. Yes, professionals on full-sized mains can do better. Michael Schumacher could also do a better job of driving my car to work, but I ain't gonna get rid of my antilock and traction control because of that, you know? So are monitors even necessary for most hobbyists? It's heresy, but maybe not . . . I still have full-sized soffit-mounted mains in my studio . . . do I use them? Not really. I never even bothered to finish the center and rear surrounds, even though the room is hardwired for them.
The next latest greatest trend will be digital wireless mics to USB dongle. TI has a new chip with CD-audio quality transmission capability for up to four channel audio. Now, of course, there is the AC 1.0 vs 2.0 issue at the moment, and TI's firmware still has some significant limitations, but this is a big step up from traditional FM-quality wireless. TI's solution will probably never be embedded in general use-devices, but I would guess the next generation of digital wireless mics beyond that will have native support on tablet devices. Now not only is the preamp gone, the cable is gone too! And the monitors can thus be wireless too . . . well, they need a power cable . . .
I mean this is going to happen and happen quickly, and if people aren't willing to adapt their advice towards newly preferred methods of recording--methods that get recordists into better acoustic spaces--then they really ought to excuse themselves from the conversation as they will be obstructionist and thus their advice will be viewed as irrelevant.
Not to pick on you, I left it alone on the other thread, but the cheap shot at VSTs? Really, in 2012, you believe that algorithms should not be used to process audio? I mean I can build a compressor or I can write a compression VST. I've done both--well, I designed the hardware compressor but stopped short of a prototype because once I added the BOM I realized no one would buy it. Probably even at half the price . . .
Stuff is changing so quickly, some of the stuff at NAMM blows me away and kicks my ass because I don't get enough time for development. The Line 6 mixer that mixes based on a physical representation of a stage, from a remote tablet . . . man, I had that idea years ago and I spent a bit of time coding a VST mixing environment, but I never finished. There are other VSTs out there like that now, but to combine that with a physical layer wireless device . . . wow. At our local concert series we are already using a StudioLive with remote iPad mixing, not only are shows easier to set up and tear down, but the mix is better and we don't have to give up seats to obstructed view. Great stuff.
I know all you say about the THEORY of digital mics is very true. However, it's rarely accurate in the real world. I stand by my frequent comments that a basic balanced-analogue output microphone and suitable audio interface is by far the best investment to make at an entry level. If I'm guilty of over simplification because I don't put in all the caveats and exceptions, so be it. But at the newbie level such caveats and exceptions add to confusion, not information.
But the thread in question was not a new investment, it was telling a guy who'd already spent $100 to spend $400 more with likely no improvement in quality he would be able to discern in the name of future expandability that he may never want to do. I object to that.
(Oh, and by the way, since I suspect the "people who have never designed circuits" part of the topic title may be aimed at me, I've been involved in the design of circuits for a number of companies. Indeed, if you Google my real name and get past the Canadian footballer and British composer of the same name as me, you'll even find some published scientific papers by major electronics manufacturers that include me on the author list.)
I realize I quoted your statement, but my feelings are principally aimed at Tim O'Brien who has been the anti-USB mic antagonist for years. His comment on that thread was completely obnoxious; yours I merely objected to your physical statement on digital microphones. I'll see if he has any remaining physical-layer objections.