I bet it's only for random match-ups. Until we are certain that Wii games have their own independent friend codes, I imagine that regardless of online region gaming, it will be possible to override region blocking. If the codes do end up being game-specific, I imagine that there will be a difference in friend code generation in each region, so that one region's friend codes will be incompatible with another's.
Anyways, it's soccer/football, so let's riot, regardless.