SSF2THD has the worst demo ever. The only mode available is 2-player local. So if you only own one controller, you can't even play the demo! What were they thinking?
What characters are unlocked in the demo? As the game is primarily competitive I can see why they did that, I would certainly prefer a multiplayer only demo over a singleplayer only one. SF2 was the first fighter I ever played, pity its such a huge download.
BTW Age of Booty is indeed another excellent, and unusual addition to the XBLA lineup. Simple to play, hard to master.