@PTravel
Please, don't get me wrong. I am not trying to say you don't know what you're talking about. I am, however, saying that if this person is trying to learn how to sing properly, timing is essential. I was going to mention such classical instances in my original post, but I figured that the OP would most likely be talking about the usual pop genres [edit: I just checked back at it. It did mention pop specifically]. Either way, the performance must have a tempo that doesn't vary constantly. In many classical/opera/musical theatre/etc. (which I also have been involved in) they have a conductor to lead the tempo and a highly trained singer that knows how to keep a steady rhythm going. To this new singer, the easiest way to learn rhythm would be to follow a rhythm section. Learn to instinctually feel the beat without having to use up too much "mental processing."
I agree with your points, but I think I need to clarify them somewhat.
"Music," at its most basic definition, is tone that varies over time. Music differs from noise in that the sequence of tones have specific mathematical relationships to each other, both in terms of pitch and in meter. That's why beginning musicians (which includes singers) learn scales, but also use a metronome. A musician who lacks the instinctive feel for beat that you mention is just as handicapped as the one who is truly tone deaf.
This is different, though, than defining who follows who in an ensemble relationship. In popular music, a drummer may play ahead or behind the beat (for effect, of course -- not due to poor musicianship). The same is true of bass players. A soloist, whether a singer or instrumentalist, who locks himself in to the beat provided by the drum or the bass will be singing "wrong." This can be heard most clearly in jazz, which is improvisational. In a "traditional" jazz performance, the ensemble will start by establishing a melodic and rhythmic theme, and then each musician will do a solo riff, improvising on the theme, and backed by the other musicians. Both the key, tempo and rhythm may vary wildly, but the piece works because the musicians are so connected to each other that they can sense where the lead is going and follow him. An obvious example is found in opera -- recitative and obligato are the singer's discretion and the orchestra takes its cues from the conductor who must follow the singer closely. The same principle applies to other genres -- in classical music the orchestra (through the conductor) follows the piano or violin soloist, in musical theater the conductor follows the actor, for "standards" the band follows the singer.
Musical theater is something I know a lot about. In my view, the most talented musicians anywhere are skilled audition/rehearsal pianists. These guys are pros at following singers, can read from the most chaotic and messy scores, and can transpose on sight. The key to what they do, though, is providing the musical backing for the singer -- it's never the other way around. That's why conducting for musical theater is a somewhat different skill than conducting symphonic orchestras. When I was in grad school, I once got into quite a fight with a conductor whose experience was confined to the latter. I had a fermata, and the conductor demanded that I watch him for the cut-off. I said, no, the cut-off comes when I finish the note -- YOU watch ME. We didn't quite come to blows, but the dispute was resolved when the director took the conductor aside and had a little talk with him -- you can guess the resolution.
The danger comes with self-trained musicians. Over the last 20 years or so, computerized music creation and production has become so sophisticated that anyone can produce as complicated a piece as they can imagine with only a standard desktop, a microphone and a MIDI keyboard. All DAWs have built-in metronomes, and the temptation is great to use it for cutting all tracks. The problem, though, is that, while it helps instill that necessary inherent sense of rhythm, it also results in a very mechanical feel. I don't know how others work, but I'll lay down a basic piano track with metronome (I have a nasty habit of speeding up without it), then turn the metronome off and do my vocals against the piano, though using it only as a guide for phrasing, and then lay down the instrument tracks with the piano track eliminated. It's not the best solution, but it does permit conforming the music to the singer, rather than the other way around.
I suspect, we're probably saying the same thing, but we're talking about two different things. An instinctive feel for rhythm and beat is necessary for any musician, and should be one of the first things a beginner learns. Once learned, however, the soloist, whether singer or instrumentalist, defines the phrasing, tempo and variations, and the accompanists must follow.
/endrant
haha I think we've answered this thread by now!