>> you're not entitled to a product that works any differently than the one they sold you.
Right, because you knew what you were buying. However:
>> Apple aren't legally preventing you from running anything.
They tried to, though.
>> Apple's request to define copyright law to include jailbreaking as a violation was denied as part of the 2009 DMCA rulemaking. - http://en.wikipedia.org/wiki/IOS_jailbreaking#United_States_...
There's a big difference between "we're not going to help you do X with your purchased item" and "we legally forbid doing X with your purchased item."
The only thing keeping companies like Apple from doing this is our insistence that they don't.