They are a subset you can rely on. It won't be as easy as Wii Sports in the future. But costs really do slow things down these days I think. There needs to be enough interest from the get go so hopefully we've yet to see the majority of the games that we'll see with the PS4 launch.
The public will get hooked by marketing and showing them appealing new concepts that might not even be that related to gaming or next-gen but starting off with that is risky since it usually hasn't been built up enough by the core fans..
The thing is you dont need a wii sports hit. You can have a wii fit hit, a brain age hit, a nintendogs hit, etc. You can tap into these other spaces in the broad market. Those games show that there are lots of proven potentially profit centers if you can find and hook them.
Edit: I do agree starting out targeting the broad market is risky, but I think its more risky to design your entire console to appeal to the core as your primary driving force. They pretty much boxed themselves in, in regards to what they can do to appeal to the broad market.