Street Fighter IV led to Super Street Fighter IV, and Super Street Fighter IV led to Super Street Fighter IV: Arcade Edition. Three different parts of the same game, Capcom has echoed the 1990s with their six core versions of Street Fighter II (original, Championship Edition, Turbo, Super, Super Turbo, and Revival). Things are a little confusing. Capcom has deemed it necessary to answer any and all questions in a FAQ.
Basically, Capcom’s trying to make it as easy as possible for people with Super and Arcade Edition to get along. The game will revert to Super’s system when necessary. Arcade Edition rebalances the characters, alongside adding four new ones. Sadly, the disc version of AE (costing $40 instead of $15, but including the whole game, not just the expanded content) doesn’t include any extra costumes. Additionally, new costumes will be available for the new characters soon after launch.
I’ll probably be buying the disc version, just to add it to my collection.