Given how well the Humble indie Bundles have done in the past (and how the current one is doing), I think their concerns over pricing are a bit overblown.
One of the reason the humble bundles do so well is that people have the option of paying more than the asking price (of free). There is no option to pay more than the $0.38 (number pulled out of my ass) amazon charges because of a promotion. Comparing the humble bundles with an app store makes no sense.
you're going to have to spell this thought out for me. i don't see how some middleman taking 80% is redeemed by the success of "humble indie bundles".