There's a whole bunch of things you're allowed to do with books that you own: sell them, give them away, lend them out -- stuff you can't do with your ebooks, by and large. Why not? Because ebook sellers characterize the transaction that you undertake when you plunk down your money as a "license" and not as a sale. You don't buy an ebook, you license it -- hence all the fine-print "license agreement" you click through at regular intervals in the course of paying for and reading books.
But everyone knows that's a shuck. Buying books is what we do. Owning books is what we do. To get a sense of how ingrained the idea of buying and owning ebooks is, have a look at this screenshot from Amazon, shown after a "license" to a book: "Now that you own your Kindle book..." it begins. If you own it, rather than a limited license to it, then you should get the full suite of ownership rights. Let's label this one "Exhibit A."