They depend on credit card infrastucture that the banks (all credit card companies are banks or owned by banks) have set up to monitor people. That way if you get a credit card number you have decent chance of having the ability to track down who you are dealing with.
Unless Ubuntu decides to try to charge people a small fee to get the ability to upload programs then they won't be able to use the same system.
This is probably something that would not be popular. HOWEVER, besides the political implications this is NOT a terrible idea, IMO. One-time fees can be benefitial for multiple parties involved.