No, I agree Mario games do have a hard core goal to them, but the truth is to most people beating the game is the goal and that is not hard at all, sure gettign all the stars is, but not every gamer is going to do that.
It is the same with Mario Bros. or Mario World, you can zip right through the games and get to the end in under a half an hour to beat the game, even if you aren't the best at it you just need to know the shorcuts. but if you want to beat the entire game and unlock all the secrets, then you do have to be good at it.
The thing is Mario is and always has been universally accepted as a casual game, not casual in the sense like Wii Sports is, but casual in the sens that any one can pick it up and play, it has always been that way before they came alogn with Sunshine and complicated things up.
On the subject of Wii Sports, and Wii Play for that matter, the game is as casual as it gets, but like Mario has goals and unlockables deep enough for the hard cores, yet simple and easy enough for the casuals to pick it up and enjoy also. (and Wii Sports is the best selling game by default not just cuz it is packed in but also because it *is* the cause of the craze in the first place)