Adding payment types to Google is hard work and has a ton of requirements around legal compliance, PR, tax, etc. The bulk of the work in adding new countries, let alone new payment types, to the Android Market is (as far as I know) tax and compliance related.
But that's the point! Who cares? I'll just buy at Google Liechtenstein, or Google Taiwan or wherever they think tax regulations are neat! They only have to care when they move the money into a problematic country, and that can probably be done in some kind of simplified batch operation.
But if an application seller accepts BTC, only the earnings by Google will have to care about taxes at all, the rest can be done in any country on the planet! Just send on the BTC to the company who made the application and let them care about taxes!
And the greatest part: the market will work for anybody, everywhere!