I don't really think that it's meanspirited at all, it's just to show what country they're in without people just assuming that they're in the US. Plus, from experience I've had in my numerous travels Stateside, other than those dicks on that io9 thread most American people seem to like accents from this way.

And, let's be honest, it's generally less offensive and more fun to have phonetic British accents than having, for example, a French person talk like Batroc ze Leapairrrrr or something.