In GTA IV, Liberty City was totally different than GTA III. It was totally remade, and the remake was much larger than the original.
Now GTA V is a remake of San Andreas' Los Santos and outlying areas. It stands to reason that the re-imagned Los Santos will have a different layout and be bigger.
On the speculative other hand...
What if this game has a tilt towards fanservice? If the game has multiple protagonists that seem similar to Vercetti and CJ, maybe it is intentional. Maybe they want to give people what they were asking for while giving them new characters at the same time. This guy might not be Tommy, but he looks and sounds enough like him when you're spraying a crowd with automatic gunfire. The other guy might not be CJ, but when you're strafing the boulevard with volleys of heat-seeking death, it'll seem like it. Since these ARE new characters though, they can have new stories. I would personally like if it was a kind of "Trading Places" story, but I digress.
Anyway, it's possible (if popular opinion is to be believed) that you have stuff like jets, Chilliad, SoCal trappings, and untamed wilderness. This is stuff you asked for. If I'm right, you also may have a chance to revisit the spirit of characters that you liked from before. It's not exactly what you wanted, but I for one appreciate the gesture. Also, instead of getting spun up about what's probably not in the game, it would probably be better to focus on what's really important, namely stealing an airplane and crashing it into that blimp.