The Market doesn't allow gift codes, there's simply no way to do anything like the Humble Bundle on Android without sidestepping the Market. Your blame should be at Google, not the Humble Folk.
Also, if you absolutely must have centralized distribution for each and every app, there are other platforms that are more than happy to provide that.
I think ultimately the solution is for the Humble people to talk to Google - and to Apple, for that matter - and say "we do this thing, it makes a lot of money, how can we do it through your servers?". If they can get the owners of the official marketplaces interested then something will happen.
They could add a slider to control the percentage of your purchase prize which goes to the App Store owner. Except you can't adjust the slider, since it's fixed at 30%. Ouch. I'd much rather continue giving those 30% to the EFF.
Also, if you absolutely must have centralized distribution for each and every app, there are other platforms that are more than happy to provide that.