Street Fighter 4 for the iPhone has been updated again and Sagat and Dee-Jay are now playable characters, the way Capcom continues to support and update this thing- it's pretty much going to be Super Street fighter 4 in all but name.
The newest update also includes GameCenter support, a 'Fight request' feature, and the original Street Fighter II music- that last one is an option for the music. You'll have to buy the track, if you're interested, from the in-game App store.