Seems a lot of Jap customers didn't like the fact they couldn't control the mech, and only customize it to give it a sort of strategy feel to the game, now US release will give us the good ol' AC gameplay 
http://psp.ign.com/articles/613/613637p1.html
With the import release, a lot of fans were left shaking their heads in confusion -- the game featured no actual fighting gameplay. Instead, it was a full-on strategy title, where you built your mech and send your AI-helmed robot into battle. That's something new for the hardcore, but it makes for a hard game to get into for new players as well as action fiends.
The North American Formula Front will diverge from the Japanese AC: FF by giving players full control of what's going in the game. Instead of just sitting by and watching, you can actually play with the mechs you make.
http://psp.ign.com/articles/613/613637p1.html