I built http://streamjoy.tv as an abstraction layer above netflix, itunes and amazon and I will attest it took quite some trickery to get something approaching a comprehensive catalog. Even things that should have been simple like using the main python library for Amazon's product api was not simple because I had to rewrite sections of the library that dealt with api throttling limits.

There are gaps in the APIs and though they can be dealt with, it was not always easy or straightforward.