You know, I both love and hate games with reward systems...I've never thought that Mario could be considered one of those games, but, especially when you're into the harder stages, it is hard to justify why you keep playing. Is repeating the same stage over and over really all that fun? Playing NSMBW with four people, I would say, fixes that problem - it is fun, and when you die (as long as there's someone else still on screen) you get a brief respite from some of the frustration inherent in those patience-testing games. But playing that same game by yourself is MUCH more infuriating, and I do find myself playing just to get more coins, unlock more pathways through the game, etc. - it doesn't take long for me to shut it off and turn away, if I'm on my own.
I like to think I play games purely for the fun factor, but Pokemon is one game that I play purely for the grind; I didn't use to, but ever since finding out about the deep mechanics built into the game, I find it hard to play just to play, focusing instead on maxing stats and building unbeatable teams. I only reached the fourth gym in Heartgold before I regressed into grinding for stats, breeding pokemon for certain natures and moves, and making very little progress for my time spent. I've beat the 5th gym, have almost 90 pokemon in the pokedex, but have spent close to 70hours playing the game...a lot of that was spent breeding pokemon, or catching the same pokemon...not nearly as fun as just assembling a team and playing through the game. I'm considering breeding my level 33 Gengar for the same pokemon with a better nature and stats - WHY?! For the metagame - Pokemon's not the worst game for sapping time (I still avoid WOW and games like it), but it can be an extremely unsatisfying game to play, if all you're doing is making your pkmn level 100, or abusing the game mechanics.
It's an interesting topic, and I'd like to read more about it - I can honestly say that I won't be buying another pokemon game, as I don't like losing my time to so much repetition...I'll gladly play the Megaman games over and over, but because I ENJOY it, not to reach a certain arbitrary level. NO MORE!!! I'm just glad I don't care about trophies as some other people out there...this type of game development needs to go by the wayside, as it really does threaten the industry as a whole. It makes me understand why people still regard videogames with raised eyebrows, due to seeing the effects they can have on people's behaviour.