San Andreas is the best selling PS2 game and it was the third best selling game ever. Right now no GTA game is even in the top ten, they're all Nintendo. I'll roughly repeat what I said before:
San Andreas is a damn good [censored] amazing game and deserves all of the praise that's heaped on it. The PS3 and Xbox 360 versions of GTA IV are at fifth and sixth respectively on the list of the highest reviewed games ever and it made $500 million in the first week which made it, at the time, the fastest selling game ever and despite what San Andreas-only fans want, Rockstar is not going to ignore this.
I'm only quoting the Wikipedia site, as i stated, what you say could be true, although i'm pretty sure MW2 broke that record, you could provide links if you want to, but your last point doesn't make much sense to me, how is GTA 4 anything to do with, the location of V and San Andreas, i'm not hating on GTA 4, nor is to blame for GTA V's seemingly only 1 city, i don't think sales of either game influence Rockstar's decision about V.
alot of fans of the series including me are dsappointed that it's set in San Andreas, but seems to be only one city, which fans are allowed to express.