If you're going to make that comparison there are some important aspects of the Humble Indie Bundle you should take into account.
- It was pay-what-you-want, with the average amount payed close to $10.
- People could divide their money among the developers and charities in whatever way they wanted.
- It was cross-platform.
- It was DRM-free.
- It and these features were new enough to generate a lot of buzz in and of itself.
Given all that I'm afraid I don't find it surprising at all that the adventure bundle isn't doing as well.
