Amazon doesn't get a lot of recognition for it, but in terms of being iterative, getting small but powerful new features out on a regular basis, etc, they really are industry leaders. This is just another cherry on an already well-fruited cake.
It's also interesting considering their core business (which they're very good at) is being an online store. They just happen to also be good at selling their infrastructure to others. (Note that Google, MS, Myspace, etc. don't do this.)
