I don't know about Wii Play or Zelda levels, but Rayman: Raving Ribbids and Red Steel have both shipped over 1 million a piece for Ubi Soft.
I'd say some other 3rd parties have probably noticed that.
This is the same schtick we've all heard before on this board anyway ... exact same thing was said about the DS. There's no question that a higher userbase will benefit any hardware makers ability to get more 3rd party support, not less.
As long as a system has a large userbase, developers will keep bringing games out for it until something is a hit, it's like flies to a light.