You'd think that, but you'd be underestimating how cheap people can be. Bastion looks nice, but I wasn't going to pay $15 for it (specifically because it's a digital download, I don't like paying more than $10 at the most for a game I can't even physically touch). I got it via an Indie Bundle for something like $4. There is the possibility that someone might be trying buying it as a cheap gift.
It's a strange quark of digital downloads, I find.Also, I can understand why a developer would want their game featured in a bundle but why would they want to sell their game this way and basically compete against their own stores?