They wouldn't release the HD version of such an amazing GTA game as San Andreas (in my opinion, the best of the best in open-world / free-roam gaming -- minus the graphics and occasional hilarious bugs) for free
You can ask for it, you can dream, but those dreams just aren't profitable. Maybe they'd do that for the GTAV limited edition (of course, then I'd have reason to buy my first limited edition game).
EDIT: And if they do such a thing, they're definitely going to be making a PS3-exclusive. That would just cause hell among those PC Gamers / Xbox Gamers (so, multi-platform pl0x).