For the people who don't know this game yet: Arcade Edition is the second addition to SFIV. The first one was Super Street Fighter, which included more characters, more stages, a better UI and more gameplay balance. AE is going to include even more characters (Yun, Yang, Oni and Evil Ryu) and some new game modes.
"Super Street Fighter IV: Arcade Edition won't be released until June, so MCM Expo London will be your first chance to catch a 30-minute preview of Capcom's brawler, as well as have a chance to play it yourself on stage. The best-dressed Street Fighter characters that come to the stage show at 11 a.m. on Saturday, May 28 will also have a chance to win limited edition MCM Expo Street Fighter shirts."
More information can be read on the Gamespot website: http://uk.gamespot.com/news/6312319.html?tag=topslot;title;5