With Fire, Amazon essentially has an independent OS. The only reason to by Palm would be that Google will not protect you as an Android maker and you need your own patent portfolio to defend yourself.
No, they didn't. The biggest sign you can see out in the open is that the Fire is running a fork of 2.3 Gingerbread instead of 3.0 Honeycomb or the upcoming Ice Cream Sandwich.
They actually forked earlier than that. Everything I've read has said the forked 2.1, which means Amazon has been developing the Fire for some time now, with impressive secrecy to boot.