Kindle Fire is an Android based tablet and is just as targetable as the NOOK devices. So either Amazon is already not steering clear, or they've paid the patent fees and are safe. So this seems like faulty reasoning to me. Given Amazon is already in the Android game, and would gain revenue throug it's App store, I'd find it unlikely that they'd have an Amazon branded WP7 device.
Agreed. Amazon is more about selling content that running programs. They need something light and customisable. Not sure Windows really fits the bill.
And because they're more about selling content, I don't see why the would feel the need to jump into the smartphone market, especially when they're already selling content on all the major mobile platforms anyway.