Nah its right on schedule. Long enough that most people haven't actually played GTA:SA in a while and are spouting off nostalgic tales of how awesome it is.
I pulled out my PS2 and replayed III, VC, and SA for a little while just to remember what they were like. SA was the best replayable game IMO as there was just so much to do. Bet on horses, fly the Harrier around abs blow stuff up with the missiles, go G ride my Subaru looking car, change out my fleet of exotics, or bang prostitutes (this isn't game specific). I played IV after and while the graphics were 1000000x10^23 better, there wasn't much to do.