You cannot give away many rights, but what right would you be giving away? A lot of the time (and I'd assume in this case), Amazon is not selling you a copy of the book. As such, the legal rights that come with buying a copy of a book don't apply. Rather, you're purchasing something like "an indefinite, non-exclusive, non-transferrable, revokable license". As I stated in my previous comment, we might want to create a small number of allowable agreements here: purchasing a copy (with the same rights that apply to purchasing a CD, book, etc.) or paying a rental fee for a specific item or library of items. Those have direct corollaries to things already dealt with in law.
Think of it this way: let's say that you bought a Zune and paid for the Zune music service. You download unlimited music to your Zune and later stop paying for the service. You have given permission for them to remove those songs from your Zune. You didn't purchase them, you were renting access to a library. It follows that you shouldn't be outraged when they remove the content given the absence of further access rental. And we wouldn't be outraged - it was part of the agreement.
Similarly, Amazon would argue (not me, but Amazon), that you're purchasing a revokable license to content - or maybe that you're being given access to a private club where you pay for them to purchase a book that they hold exclusively for you for unlimited time. However, you can be completely removed from the club and, as such, your access to said book. Think of it this way. You join a club which houses all of your books in a building. When you want to read a book, you go to that building. You have exclusive access to your books (unlike a library) and you have them forever, but you can't remove the book (in return, they guarantee that it won't wear out or break). However, part of the terms of the club are that you won't smoke in the building. If you smoke in the building, you'll be kicked out of the club and lose access to the books you have in the club.
Where it becomes nebulous is the Kindle. The Kindle is your kindle, but is the kindle the club or the key to the club? Let's say the key is your property and they can't make you surrender it - it's your property that they have no right to. Well, they can still change the locks.
I know it feels like purchasing something, but with DRM we can already see that we don't have the same rights as with a physical copy. With a CD, I can sell that CD to a friend or a record store. With an iTunes song, I can't. One can argue that I have first-sale rights and I usually argue that it should be treated that way, but dispassionately looking at the legal situation, it's murky. Remember the rumor that some actor (Bruce Willis?) was going to sue Apple to get a judgement that he could pass on his iTunes-purchased music to his heirs? We were excited about it because it would have established first-sale - if it were already something no one questioned, the rumor wouldn't have existed. If the Kindle book was really your copy, you could sell it to a friend. Since you cannot sell it to a friend, it's unreasonable to assume that every other right you have with physical property applies. I'm not saying this is how things should work, but describing what exists.
Heck, the circuit court in the United States just ruled that if you purchase an Omega watch manufactured overseas, you cannot re-sell that watch when you don't want it anymore - Omega can block that sale via its copyright rights. Likewise, if you purchase textbooks overseas, you can't resell them in America (again, according to courts). The Supreme Court is reviewing this case right now. So, it certainly isn't so cut and dry given that the second highest court in the US isn't holding by the first-sale doctrine for these watches.
The difference between this and breaking into someone's house to steal their books is that you own the (copy of the) book. It's your property. It's irrevocable. I'm not arguing that Amazon has done something good or that this is the system we should want - it isn't. But there's a difference between how we think the law should be and how the law is. And that's an important thing to recognize if one wants to change things.
It should work like how you say. That doesn't make it so. Right now, we aren't purchasing eBooks from Amazon, we aren't purchasing songs from iTunes, etc. They're trying to maintain in control of the relationship and to make it revokable from their side. It shouldn't be. In common law jurisdictions (US, UK, Ireland, most of Canada, etc.), this may happen through court precedent, but it's hardly something that's been cast in stone right now. Personally, maybe a simple law about purchase and rental of electronic goods might be in order. Something along the lines of "you can rent or provide temporal access to content which will be removed after the access period has expired or you can sell a copy of content with the same rights that purchasing a physical copy would confer. Other arrangements are disallowed." But we don't have that today. Maybe this story will have a court case in which a court rules that you can't offer revokable access if an item has been paid for as an unlimited time purchase. But we aren't to the point where we can definitively say that Amazon acted illegally. Amazon acted immorally - that's why we're outraged. It's her content that she paid for and she should have access to it. If it were physical property, Amazon would be dealt with swiftly. However, the rules for physical and electronic content aren't the same.