I've never thought of Roger as an idiot. A bit slow, yes, but not a brainless klutz the way some fans depict him. Moreover, I think he's well-aware of the fact that he's not the brightest bulb. It's been awhile since I've played Space Quest 6, but I don't recall anything in the game that made me think he was an idiot. Quite the contrary, Roger came off as a sarcastic, slightly depressed guy, much more so than in the previous games. This makes me think he knows more than he lets on and to be quite honest, when we look at his life, he's got plenty of reasons to act that way.
Alternate character interpretation, perhaps? :|