Using IGN's release dates lists between now and the end of the year there will be 101 third party Wii games released, 55 third party PS3 games released, and 78 third party XBox 360 games released; this is not exactly the best way to determine third party support but it does demonstrate something ...
In 9 months the Wii has gone from having the Worst third party support to having the most third party titles available for it over the holiday season. Certainly, in terms of quality most of the Wii's third party software is crapware and the best development teams are releasing their games for the XBox 360 and PS3 this holiday season but (in all likelyhood) these third party developers began work on these titles between the time the Wiimote was announced at TGS2005 and E3 2006; long before the Wii was released and the popularity was obvious.
Even if the Wii starts to sell slower than the XBox 360 and PS3 in 2008/2009 the (reasonably) large userbase and low development cost will still give it an edge in maintaining and gaining third party support; if the Wii maintains its sales edge it will start to dominate third party support like so many leading consoles before it.
