sorry to reply to a thread that's been dead for ages, but i thought some people might be interested in this
Rockstar North wrote the code for GTA:VC on the ps2. and they are writing GTA:SA
but the conversion to the Xbox was done by Rockstar Vienna
and from what i've heard, they had a lot of trouble with the port because there were lots of last minute hacks that R*north put in to make VC work on the ps2 that totally failed to work when ported to the xbox and so had to be re-coded.
so i wonder if another reason for lack of mention for any other platform release anytime in the near future might be that, having see the difficulties involved with the VC port, they'd rather take their time this time around to get it right without the panic of trying to hit a deadline