My exchange rate will only increase as Bitcoin becomes more popular. There are practical limits to the popularity of Bitcoin. Sure, potentially it could be run on every functional computer around the world, but from practical perspective, that will never happen. The swarm is currently pretty small, so when a few new users join, there is a large effect on my exchange rate and it increases fairly quickly. As the rate of growth slows or reverses and as my exchange rate average increases over the next two years, the exchange rate will steady out with only very small increases AND decreases every day. As for the impending doom and gloom you're prophesying will accompany the decreased payout in a few years, all I have to do is add a little multiply by two to my exchange rate calculation and the problem is solved. The exchange rate stays constant and everyone is happy. In any case, hopefully by then there will be other ways of calculating the value of a bitcoin other than my single solitary exchange service.