This is almost certain to cause an increase in piracy as owners of now-obsolete Nooks turn to torrent sites for books they otherwise would have purchased.
It's a situation that takes the usual morality of theft piracy question (which people have many different opinions on, both regarding the question itself and the possible answers) and makes it harder: What happens when people can't make a "moral" decision, because you've taken away their option to do so?
The people who really lose here aren't the ones who go to the torrent sites; they at least still get what they want. It's the people who don't know they can do that. Those people? They're just screwed.
Hopefully they get collectively upset enough to make people notice. We'll never be rid of this kind of problem, but perhaps it can be made less painful if enough angry support calls are made.
> It's a situation that takes the usual morality of theft piracy question and makes it harder
No, it just highlights the fact that you cannot assume that illegal implies immoral.
A little piece of fine print claiming that your purchase was actually an indefinite rental that can be unilaterally cancelled has only tenuous legal power, and absolutely no moral authority. If you bought an eBook in a transaction that was essentially the same as buying a paper book, then you've fulfilled all moral obligations for compensating the author and publisher. No amount of legal shenanigans will create a moral obligation for you to censor that book from your personal library, any more than a legal action can create a moral obligation for you to burn your personal paper books.
There's a problem here, but it's not a moral dilemma, it's just another imperfection in our legal system - an indication that we need to change the laws.
