Yes it can Vagrant, but it'll be closer this time around - due to the fact Metroid will be more FPS esque and because of the game drought we are suffering, which Metroid - not Smash, will end.
As for SSBB Lover your argument is extremely weak. If you think that WiiChat users are the average games consumer you are incredibly wrong. Anybody dedicated enough to gaming to read and post often on a forum is NOT average. They're verging more towards the "hardcore crowd". This is one of the reasons SSBB is so popular here. Your going to have to come up with something more concrete I'm afraid.
Vagrant is correct history does indeed tell us Smash will sell more. But the timing of the releases is different this time. Metroid is crucially released first just at a time people are looking for a killer app. More fps controls will also pull it more mainstream as opposed to the GC games. It's going to sell much better than Prime 1 or 2. I think that, especially when considered with the large Wii user base, is clear.