GTA3 was set in the 90s, Vice City was set in the 80s, so, logically, San Andreas will be set in the 70s. How much you wanna bet that in one mission, you'll be in a dark green fastback "Stallion" chasing a black "Sabre"?
P.S. PS2 sux, PC rules, Xbox is a'ight. Rockstar needs to get their head out of their ass and ditch Sony already. From the get go they limit themselves to the PS2's miniscule 32Mb of RAM, and then cars disappear whenever you turn around, even in the PC version!