Well, Amazon TELLS you that you lose the right of first sale. That has yet to be tested in court. EVERY industry (seriously, try to find one this isn't true for) has tried to kill the secondhand market in their particular corner of the economy. And every. single. one. of them failed utterly. Digital goods purveyors are going to fail just as spectacularly. It will require lawsuits, of course, but eventually digital property will be respected as actual property.

Right now, when you purchase a digital good, you are quite literally paying for nothing. You're giving money to a company and basically asking them to do you a favor and give you access to some content. Nothing in the "license" you agree to obligates them to actually provide you with ANYTHING. It conveys absolutely no rights to the purchaser and, just as importantly, places absolutely no obligations on the "seller". As it currently stands, it's basically just a giant sham with consumers acting in good faith and waiting for some CEO at Amazon or Apple or Barnes and Noble or somesuch to try to eke out a little more quarterly profit by doing something like requiring consumers to pay more to unlock content they already "paid for".