I disagree, the two games are made by two different branches of Rockstar - What we know for certain is:
1. They've been working on this game for at LEAST a year. (more likely 2 or more)
2. They've made hints at it being in San Andreas OR Vice City. (I think a new city won't happen)
3: As pointed out earlier it's GTA V - Not GTA: SA 2. So there is a massive improvement in this game to earn it a numerical title. This could be playing multiple characters - or it could mean it will debut on the next-gen consoles. (I find next-gen consoles impossible to imagine, as the Xbox 720 won't be unveiled until 2013 - and sold around 2014, and that's a LONG time to wait considering the trailer is out in 7 days.)
Enjoy reading more speculation about where it will take place - it seems Washington D.C is really popular! I might be wrong about the new city thing...
Click here.