Ehh... we could discuss this for the next century, but facts of the matter are that to objectively state whether the whole "third-party doesn't sell on the Wii" point of view holds water or not, we'd have to browse through every single NPD, Media Create and god knows what other statistical data for each year the system was on the market, compile that mass of incomprehensible goo into a chart and then calculate if it was worth it or not. What we have are symptoms - little high-profile games and large gaps between first and third party software sales, so we can make a safe assumption that third-party titles didn't do too well, but it's not an objective fact. Establishing that is a humongous amount of work that none of us are willing to go through - probably weeks if not months of research.
Again, the Wii suffered from the shovelware problem wheras high-profile releases were few and far between. There's a difference between exploiting an admittedly large target audience with games studios made on the side with zero effort put into them and actual support. There's a zillion of Wii games out there, sure, but that doesn't mean that they sold very well on a per-title basis - maybe they released so many crappy ones to rake in profits from cumulative sales, "quantity over quality" style.
