The first comic I read with Abomination in it never mentioned his real name, where he came from etc, so I never imagined his voice as having any accent at the time. With that first impression staying with me even after finding out his origins I cant say I'm too bothered he doesnt have a russian accent.
I am curious as to why he would have a British one if he is part of an American special army force though (it's not like Roth hasn't done American accents before).
I don't know, I just saw Roth in a HBO mini-series called Tsunami: Aftermath he had a british accent, but it was so light it might as well have been an american one.