There have been two "official" reasons listed and I believe both. One is that different color combinations go over better in different cultures. If you've seen some of the international balls out there, that's easy to believe. The other is that some of the covers are a little different (milder in most cases). I don't know whether that's still true but it has been true for some balls in the past.
I'm sure, however, once it became apparent to the domestic manufacturers (especially Storm) that ball fanatics want one of everything, that it might be a good idea to let a few overseas balls leak out. Columbia made some beautiful overseas balls prior to the Ebonite buyout (specifically the Ricochet Revenge) that would have gone over very well here had they been released in the U.S.
As far as whether they perform better, I can't say in general. I can tell you specifically that Storm's Xtacy Domination is in a league of its own in terms of the amount of boards it will cover, for me. I don't know that I'll ever see lane conditions that will allow me to throw that ball without having to start my approach on the adjacent lane.
Jess
