Actually you do have the RIGHT to unlock your phone, but if you do Apple has the option to not support you. That said I think Apple crosses a line when they outright void your warranty for a software change. For example, from what I have seen, the phone has a reasonably high rate of failure on screens. I'm not talking about BS screen quality issues, but rather real defects that result in the complete or partial loss of touch sensitivity. I'm not sure how they justify absolving themselves of responsibility for physical defects.
I admit that this could be spun as a tricky issue in that some applications really can cause failures (like burning out the vibrator from excessive use) but unless they can show that a mod resulted in the issue it should be on their plate to rectify it. Let's not get into issues of "faking" dead screens in software, since as a consumer I don't like business models that presume I'm committing fraud.
I don't think that Apple has any obligation to go out of their way to support hacks; however making changes for the purpose of breaking something is not acceptable. I'm not saying that this is what happened, since a lot of what was changed has good justification as to improving the phone, but I don't think anyone would argue that a large portion of the changes are directly intended to restrict the owner from accessing it. I don't care if breaking "functionality" is legal for Apple or not, but as a consumer the arbitrary lock down of any device from it's owner is disappointing and makes me wary of Apple polices and products going forward.
I guess the whole point of this is, just because something is legal, doesn't make it right.
Try modding your car engine, then go and complain about anything else going wrong in the car. I guarantee you they would say the same thing Apple said about voiding the warranty