I don't like this decision, but not really surprising. Working in IT several of the systems I work with are used under a similar licensed usage agreement.
The solution is simple. If you want to jailbreak a device don't buy a restricted device. There are plenty of good Android devices out there that will always be legal to do whatever you want with. Some OEMs will even supply you instructions on how to do it.
Whatever you do, don't buy restricted devices and then complain about not being able to legally root them. In addition to looking like a fool, you are not helping your cause at all by doing so. Amazon and Apple do not have monopolies. Exercise your free will or they will never change. On the contrary, they will continue to lock things down even tighter wherever they see a chance to profit from it.