First of all, that's a pretty big accusation to level at someone on public record: are you 100% certain that the graphic assets have been lifted pixel-for-pixel? Second, I agree with you on the legal point: it's much easier to 'protect' visual assets than it is a game mechanic. However, I dispute the fact that ripping off someone's game mechanics is, somehow, more ethical; in both cases, you're simply copying someone else's work and passing it off as your own. Just because one is easier to define, and therefore protect, in law, doesn't mean they're not both pretty nasty ways of operating.