EA seems to agree that it would be a weird choice, which is why it isn't actually doing that. It turns out that the quote was mistakenly taken out of context: at the Goldman Sachs conference, Pleasants talked about EA's planned MotionPlus sports games and Dead Space at around the same time, and somehow in the trip onto the Internet, the two subjects became conflated.
Update: Sean from GameCyte has helped us clarify the source of all the confusion: not a misquote, but rather a mistaken statement from Pleasants himself. He did say that Dead Space would use the MotionPlus peripheral, which has since been confirmed not to be the case.