When Niko is talking in the intro he says "and then I spent the next 7 months with you fine people and I forget"
Which means, the game was suppose to come out in October, but they delayed it until April, and you do the count and it's 7 months.
Another theory of mine is I believe the next GTA will be in Vice City...
I thinking they're just getting what they did in the old consoles and remodeling new ones...
Also, another would be that Rockstar made Playboy X and Dwayne to be similar to CJ and Sweet
CJ is Playboy X after he got the mansion always thinking about himself and money
Sweet is Dwayne always thinking about the hood and the old days...