Instead of using either as a point or counterpoint, isn't it more productive to say that traditional third party core games can indeed sell on the Wii, but it is not a foregone conclusion that they will sell well across any genre and demographic as long as they are of quality and is marketed?
The way I see it, the Wii has the highest user base, but definitely not the highest user base across all demographics and fan bases. This is very obvious and hence the discussion would be more interesting to analyze what sorts of franchises and genres could do very well on the Wii but are not on it yet. Also, what genres and franchises would actually be counter productive to attempt to put on the Wii?
To illustrate the point, I'll suggest that things which could certainly do well on the Wii: Kingdom Hearts, Final Fantasy Tactics (Fire Emblem sells!), more Monster Hunter, Dragon Quest, maybe Phantasy Star. Things which should never even be considered for the Wii: Ryu ga Gotoku, Metal Gear Solid, Ace Combat.