Well, in some cases they have more. For example, my daughter is to the age she wants to catch up on all the Monty Python and the Flying Circus episodes. Netflix dropped it. She can still watch on her Kindle Fire with my Prime account. I'm more in to documentaries or old movies, and don't really care about new release movies or TV shows. I was surprised to see some pretty good movies in the free list, though! I haven't seen MI-III (not even sure I want to), didn't expect to see it free.
I work from home, so I just checked it out. To me, the picture and sound are superior to Netflix. I can't guarantee 5.1 because I'm in the middle of setting up my new movie room, and haven't hooked up my rear speakers yet. In fact I had to hook up my fronts to demo
Anyway, receiver reads PCM (Amazon isn't bitstreaming) and the sound is fantastic. Center speaker sounds right, can only assume 5.1 is 5.1. Con - the app doesn't seem to work right with my Logitech Harmony One, and I'm assuming it won't with the official BD remote - I'll test the BD remote later.
I know $80 per year isn't a lot of money for Netflix, but it angered me when they dropped the DVD in the mail as part of the subscription, and I am betting I don't need Netflix and Amazon Prime at the same time now that I have an easy way to watch on my home theater system.
I have PlayOn on my media server, betting it'll work on my iPad, so I may have a full solution to rid myself of an $80 per year bill.