Amazon has always made a point of not building services on top of its Cloud offerings that directly compete with its users. Cloud Drive sets a precedent for them as the first time they've gone against that principle.
There are lots of "low hanging fruit" companies that were built on the understanding that Amazon wasn't interested in implementing that stuff themselves. There's no debating that this will make Amazon a ton of money. It remains to be seen, however, how much it will cost them in developer loyalty and businesses that never get built because "If they did it to JungleDisk, they'll do it to us".