I would argue it's not so much the rewards, but rather the feeling of progression towards a reward. I used to have a terrible problem where I would just waste

I would argue it's not so much the rewards, but rather the feeling of progression towards a reward. I used to have a terrible problem where I would just waste entire weekends playing a Civilization game, not because I was being rewarded, but because I could tell I was progressing towards some form of in-game victory. As soon as I felt like this wasn't the case the game just lost it's zeal. It's still a reward, but with more subtlety. Ironically enough I'm actually a game developer myself and have used insights such as these to create a web app that turns business development and customer validation into a game. Seems to be working, albeit by my own admission it's a tad strange.