Do you have numbers to back this up? Because I thought that front-page placement on the App Store is much more desirable than to be in any of the charts. (Of course, being #1 in top-grossing is good - but not only because it increases visibility :)). Even in iTunes, where the charts are visible on the landing page, only #1 even shows an icon, compared to about 50 curated apps.

I think the big difference is that people buy a game on Steam to be immersed for a few days, yet people buy smartphone apps to bridge the gap between two Twitter mentions or subway stops.