This is the same misguided argument, repeated ad nauseum, by folks with axes to grind.
You purchase an ebook tied to a specific device -- those are the terms; if you don't like the terms, don't buy the ebook. In fact, you have the right in most cases to attach the ebook to up to five devices. You can loan those devices as many times as you like and to as many people as you like. That's exactly the same -- arguably better -- than a pbook lending experience because you actually can buy once and get five copies.
And, if you lose your copy? Download it again. Try that with a pbook!