Interestingly enough, the reason for the similar sound, both sonically AND genre-wise, is that humans prefer sounds they're familiar with. They associate it with safety. And, as the majority of listeners are passive and couldn't give a shit less about lyrical or emotional content, it makes more sense for the radio to play things people feel instantly comfortable or familiar with. The radio is in the business of selling commercial time: the purpose of the music is to fall into the background just enough to prevent you from changing the channel. Whenever you hear something genuinely new, or at least unfamiliar, you have to make a conscious decision whether or not you like it. Generally, you've got a 50/50 chance you'll like it enough to keep listening. However, if the newest "Fall Out Boy" or whatever song comes on, and it has the same sound sonically, as well as generally the same lyrics, song structure, chord progressions, etc., 99% of people that liked the LAST Fall Out Boy song will like the "new" one. Thus, they stay tuned in for the commercials, which the real reason for radio to exist in the first place.
Before any of you argue, do some research: these are facts, not opinions.
Steve, can I voice a dissenting POV without it being called an "argument"?
What you very eloquently stated is the justification given for the actions of those in the music and radio industry. To put it shortly and bluntly, all it says is "Hey, don't blame us, it's the listener's fault." That's hogwash.
If it were true, we'd all still be listening to Frank Sinatra.
It's not the listener's fault. it's the fault of those making the records, on both sides of the glass. The reason things tend to sound the same is out of caution/trying to play it safe, an attempt to make science out of something that is NOT a science, and a lack of creativity on the part of those who's job it is to be creative.
Caution and playing it safe in that everyone is trying to catch a single bolt of lightning twice. Or rather, that they see that a bolt of lightning hit over ther, so everybody runs over there to try and catch it, even though the odds are that the next 100 bolts of lightning will hit elsewhere. This ignores the fact that - unless you're talking about the Sears Tower or something like that - lightning tends NOT to strike in the same place twice.
Take all your biggest acts of the past half century, people like Sinatra, Elvis, The Beatles, Bob Dylan, Springsteen, U2, etc. etc. etc. They didn't become the world's favorites because they sounded like someone else. And at the same time, those that tried to copy them while they may have had some modicum of success, for the most part the only REAL success they had was when they imprinted their own unique style or sound on their work that separated them from their predecessors or mentors.
Faking science by trying to treat the art form of music - which is all about emotion and expression - as if it were a formulaic science. No matter how much the sales departments at the radio networks would like to believe otherwise, it's not a formulaic science, and never will be. It is a creative art.
But you'd never know it was a creative art by listening to the multitudes of mySpacers and home rec'ers who constantly come on here and ask the questions, "How can I get my recording to sound like _________". Whether "_______" is referring to a specific artist or band, a "commercial sound" in general (whatever that means

), or simply trying to be as loud as the Joneses, is just different wallpaper in the same room; that room is in each case simply "trying to sound just like the last guy or the next guy".
So let's stop our pretense of self-righteousness on both ends of the recording contract and stop blaming the listener, OK?
G.