I was talking to a professional musician once who mentioned that the first part of the recording that is done is the percussion track which is laid down by a studio drummer who he described as a human metronome. I didn’t get a chance to ask him, so I’ll ask you, why not use a machine? Is there a tonal difference or some other way to tell if it is human or a machine?
It used to be very easy to tell a drum machine from a drummer, but as the technology gets better it gets harder and harder.
I guess the knock against drum machines is that they are too perfect. If you listen carefully to a song and try to block out everything but the drums, there is a distinct difference between pop and rock.
Rock drumming sounds more like jazz drumming where the drummer sometimes lags a little behind or gets a little ahead of the other instruments. This generates a certain amount of tension which can add to the emotional impact of the music.
Pop music can sound a bit sterile with everybody completely in-sync all the time.
Of course you could program a drum machine to drop a little behing or step a little ahead of everyone else, but then even that could get a bit programmatic.
Particular performances can be particularly great because the musicians made the perfect adjustments at that time and that place.
Programming any of that ahead of time and expecting to pull it off would be near impossible IMHO.