This sort of thing matters to a lot of people, so here we go. According to Matt Casamassina's blog, Platinum's MadWorld runs at 480i. Not 480p.
Buy it anyway. It looks awesome. As Matt says:
You must still buy this game, but this omission raises an interesting point. Usually, lack of 480p support can be credited to developer laziness. No way such a claim can be leveled at Platinum Games or MadWorld. This is a AAA developer which constantly pushes the artistic limits and MadWorld is the latest proof of that. I'm wondering, then, if the studio simply wasn't aware that 480p is "kind of a big deal" for a chunk of Wii owners.
What's the difference between an "i" and a "p," anyway? It's out next month.