However, your experience is not of an equal level to those who have spent extended time with the game learning the depth each game offers.
For instance:
http://www.youtube.com/watch?v=QwFPwhnMWiE
The game designers made these things possible, and to reduce it to a "mildly entertaining diversion" is a disservice to those who have spent time getting to know the intricacies of each game.
I think it's fantastic if some people out there really like the games in Nintendo Land. Honestly, it's super. However, I'm not sure if pointing towards the existence of people looking to master a game is in and of itself any sort of an indicator of a game's quality. I'm not suggesting that it means nothing. However, I don't know if I necessarily agree with your point.
As a for instance -- and let me preface this by saying that I'm not suggesting that Nintendo Land is this shallow -- I once wasted an entire day trying to master some simple Flash Putt Putt game striving for the perfect 18. After hours, I had gotten to the point where I could hole-in-one every hole but 2 with ease. A couple of hours later, I knew what I had to do for those two other tricky holes. And finally, after about 8 hours, I did it! The perfect 18!
That story indicates that I had some fun with the game, and that there was definitely some skill involved in mastering it and memorizing the power/trajectory in shot-making. But I don't necessarily think it undermines anybody who doesn't think that there's a lot of meat there. And I think that's how I feel about Nintendo Land.
The existence of a neverending battle for the Donkey Kong high score doesn't have me convinced that it's a great, deep game to this day deserving of countless hours of practice to become the next Billy Mitchell or Steve Wiebbe or whoever has the record. As such, if something like that released today, I wouldn't be convinced that it was a great game.