Before poo-poo'ing the idea, consider that a conspiracy isn't required for Google to be unconcerned with paid app sales. Android only exists because Google was afraid of being cut out of mobile search advertising. Their priority has been getting a competitive OS with a prominent Google search box on as many handsets as possible. Paid app revenue is something of a sideshow. (Even with paid apps, Android isn't going to turn a profit in the short term, so why worry about minor revenue streams?) I'm sure Google doesn't want a shitty, disorganized app store that can't collect payments or rampant piracy, but they aren't exactly hurting Android yet, so why should they worry about it?

Edit: Even worse, Google apparently doesn't get any revenue from paid app sales. Their 30% cut goes to the carrier. (Thanks gregholland!)