No, if the games aren't selling they're doing something wrong. "Only Nintendo games sell on Nintendo systems" is a lame excuse to cover their rears for bad decision-making.
I will say that making a hit on Wii is not going to be exactly the same as making a hit on the other consoles. A direct remake of a game like Final Fantasy XIII probably won't match the HD sales because Wii owners aren't looking for an interactive movie - type game. That doesn't mean they aren't looking for a proper sequel to Final Fantasy I or Final Fantasy IV, though.
On the other hand, with 64 million owners, I don't understand why third parties are giving us spin-offs developed by their B-teams. There are 10-million+ selling game ideas just waiting to be developed on Wii but the big companies don't even seem to be trying.