The Sony's have the best track record with PDFs but they still don't do a great job. Harry will eventually show up and tell you that PDF's are meant to be read at a specific size and e-readers are not able to match that size.
As for Amazon deleting books, it happened a couple of years back. Everyone who had the books deleted got a gift certificate for a free book and the option of having the book returned or a second gift certificate for a book. The PR was pretty darn bad, I seriously doubt it would happen again.
Not to mention, people who had downloaded a copy of the book to their desktop where able to reload the book safely when it was removed. So if you do the smart thing, save all of your files to your computer, you would be fine.
I type this less because I am going to convince you of anything but more because I don't want others to think that you are right.
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