Mario used to be milked to death, since there are about 200 Mario games, however, Nintendo stopped milking the franchise.
Ratchet isn't "milked" either, there is now a Ratchet title every two years, I don't ocnsider that milking.
However, I would still like them to have bigger changes between each game.
Bet with Dr.A.Peter.Nintendo that Super Mario Galaxy 2 won't sell 15 million copies up to six months after it's release, the winner will get Avatar control for a week and signature control for a month.