One of Blow's comments in particular I found fascinating:
I feel like unearned rewards are false and meaningless, yet so many people spend their lives chasing easy/unearned rewards. So there is a very conscious decision that you only get collectibles in "Braid" when you solve a puzzle, and you only get one per puzzle. Some of the puzzles are easy, some are hard; but you did something very explicit to get the reward. It’s not like "Mario" and every other game since then, when there are gold coins sprinkled everywhere, and you get them just by walking along a path or jumping up to some blocks, and that satisfies your reward-seeking reflex for now and pacifies you into continuing to play the game.The difference between "frequent tiny rewards" and other forms of reward schedule is the old psychological observation that people aren't good at realizing that a lot of very small things, in volume, can add up to something very large.
I actually think that Skinnerian reward scheduling in general (which you see in most modern game design, MMOs being the canonical example) is unethical and games should not do it -- scheduled rewards, to keep the player playing, are a sure sign that the core gameplay itself is not actually rewarding enough to keep them playing, and thus you are deceiving your players into wasting their lives playing your game.
This is the mechanism behind eBay's success -- they don't have to add but a tiny amount to each transaction for the total of those transactions to become enormous. (It's also the principle behind taxation. Spreading out takings over many people (and for individuals, over each paycheck) generates large revenues and allows statements like "but it'll only cost you less than a postage stamp in additional taxes -- surely you can spare that much, can't you?")
So the question is whether tiny rewards are less ethical because they have this recognized psychological effect of changing our behavior in a way that we tend not to realize.
That said, is it always bad? The turn-based games considered the best ever -- games like Civilization -- are said to have a "just one more turn" effect. "Just one more turn to see if I can finish building this road, and then I'll go to bed..." at which point you realize the sun is coming up.
Designers of these games consider this effect something to try to achieve. So are they just giving us the intellectual entertainment experience some of us obviously want? Or are they wrongly exploiting a predisposition to addictive behavior?