I'm not surprised that TakTOM Metroplex speaks English. The Fall of Cybertron game in Japan does use the same Anglophone voices (e.g. Peter Cullen as Optimus Prime etc.), but with Japanese subtitles. It also wouldn't be too hard for TakTOM to simply include a translation of the lines say on the instructions somewhere (I'd be interested to know if this is the case or if they're solely relying on people's exposure to the game).
Also... don't underestimate the power of fanboys. Some Japanese fans' knowledge of English comes almost exclusively from video games. When I was a uni student in Japan, I knew some guys whose English virtually entirely came from Diablo... when I told them I was from Australia, they'd say, "Oh, I know some English... "Fresh meeaaat!"" ... uh... 'kay.

It's not too dissimilar from Western fans of Japanese games and anime whose Japanese vocabulary almost completely comes from games and anime.
These are gateway words into more hardcore language-learning.
