Well Sony has always relied on 3rd party software, that was the key back in the PS1 days was to get as many dev's to develop for their system. Same thing with the Xbox but I guess MS didn't try hard enough until the 360 came out with guns blazing. If you combined the amount of PS3/360 3rd party games in that graph it would equal roughly the same amount as the Wii's 3rd party software, but the HD twins stats would totally trump the Wii's.
It's not a bad thing either for Nintendo to be pushing out massive amounts of software because they make money out of it, I think complaining about it isn't going to do anything about the 3rd party situtation on Wii either. Dev's need to understand the proper formula for the Wii like Nintendo has and just go with it.