[quote name='daroga']Hmm, call me slow (cause I am), but I just realized how odd the 4 numbering is.
Were Vice City and SA supposed to be "add-on packs" to 3? Or did they just start counting over with the reinvention of the series in GTA3?[/QUOTE]
Basically each number represents a series. And at each new number the game recieves an upgrade.
First GTA, then GTA 2 came out and it had upgraded graphics and design scheme. Then GTA London came out, and it still had the same look as GTA 2 just a different area.
Then GTA III was released and it was a massive upgrade with a whole new design, new game engine and graphics. Then VC and SA where released they use the same graphics and engine just new weapons and vehicles and area, but all in all running the same engine as GTA III.
Now with GTA IV it will be a whole new engine with overhauled graphics.
Just think as every # in the series as an upgrade, where as I guess you can call london, Vice city, and san andreas expansions. Where they don't add anything new visually to the series.