one explanation sort of hops to mind for me, though it is a pretty flimsy one. I see it as alot of game and gaming componies being based in the US and Japan (I realise that there are developers based in Europe and the companies probably have offices there, but just roll with me a bit...), so they get the games first. Games out of japan take forever to hit the US and the reason is usually translations, both subbs and the dubb, which adds a bit to release time. as for Europe (keeping it as a generalised reagon does have a purpose i promiss), there are alot of different laguages in a reletivly small area, and so while waiting for the games to be translated into all those different languages, the companies hold off on releasing in Britton and the UK to avoid A) more realease dates and B) logistic issues. It all kinda boils down to saving money and time i guess....
As i said, this is flimsy reasoning, but its all i could come up with... feel free to think up something else, but dont go abusing me over anything i said ._.