Depends who does the voice acting, really. Game developpers located in the US tend to use american voice actors most of the time because they're right there. It seems to me that unless a studio does the voices themselves there tends to be only 2 or 3 companies they ever use. Heck, it seems like with import dubs you either get Canadians or Americans, and you can usually tell by if you hear Kirby Morrow or Steve Blum. The big difference is if you get the latter you're also more likely to hear Jennifer Hale and the occasional celeb.
I should point out that there's no such thing as a 'lack of accent.' Anyone who speaks a language has an accent. English alone has Canadian English, American English, UK English, and probably others that I can't think of off the top of my head. Irish English maybe?