All they should do is void warranty if someone tempers with the OS. Same for books.
It's a very simple point: there is a difference in the rights you have over hardware and software just as there is a difference in the rights you have over a book and the contents of the book. Pretending that the rules of one should apply to the other is nonsensical.
The reason this distinction is important is that many people claim that Apple is impinging upon their rights with the restrictions built into the OS, but they don't actually have any rights over the OS and ownership of the hardware does not grant them any. By analogy, owning a book does not grant you any rights over the copyrighted contents. People readily understand the latter, but seem to violently reject the former.
All they should do is void warranty if someone tempers with the OS.
That is all they do. Why would you think otherwise?
Not true. Read a bit about "ibricks": http://bits.blogs.nytimes.com/2007/09/28/more-on-apples-late...
I understand that people want Apple's software to allow certain things, but I think stating it as if Apple is impinging on the user's rights because it does not is a dishonest exaggeration.