RE4 could have staying power because I'm sure most of the Wii demographic never played it originally. It's amazing, it's well-known, it's cheap, and there won't be many great games available this whole year, esp over summer.
And I know a lot of gamers who skipped GC but do have a Wii. I don't think the Playstation 2 version will really hamper the Wii ver sales much either.