Well to be fair what they're adding with Super Street Fighter IV is enough to be a new game on its own. About 10ish new characters so far and new gameplay mechanics. Sure they could release that as DLC but it'd be pretty damn big. Besides this really shouldn't be that big of a surprise, Capcom did it with just about every other Street Fighter game out there.
Well at least this is an excuse for me to get IV on the PS3, even if its a different game.