I still remember that Bioware/Black Isle took over a month to release the English version of Baldur's Gate/Planescape/Icewind Dale after the release of the US version, just because of the required translation as they claimed. I didn't check if it was true though and see if my version is British English then. But assuming it is true, there are some companies who do put in the effort to creat a US and British English verision.
Personally I agree that an effort should be made to translate it to US English, it goes for quality and care. On the other hand as a non-native English speaker, it doesn't influence my gaming at all, not even if the two of them were mixed in one game <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />
