The first problem is that while jailbreaking is now legal, it is also legal for Apple to push a change that happens to break jailbroken phones. Apple doing this could create liability and/or negative publicity for any company that had sold such services on a wide scale.
The second problem is that lawyers will be trying to find a way to create the old result, and are likely to succeed. For instance Apple's restrictions against jailbreaking are almost certainly in their shrinkwrap license contract. Therefore the fact that they can't throw the copyright book at you, doesn't mean that you're necessarily legally in the clear to do it.
Apple has proven willing to brick jailbroken phones in the past. They didn't suffer any liability, and didn't get very much negative publicity. And it did wonders for maintaining the wall around the walled garden they are trying to create with the app store.
Given this, I see nothing to suggest that they won't do it again. And any company who suggests otherwise is taking a definite risk.
Apple has proven willing to brick jailbroken phones in the past.
Have they?
The famous case of "bricking" back in 2007 was not related to a jailbreak, but was a botched unlock tool[1] that corrupted data in the baseband firmware. The corruption then led to problems with an update. Apple issued a warning when the update was released saying it would affect unlocked phones, and I can't imagine this is out of malice so much as it is out of Apple's pre-release testing activities revealing problems.
If it were an intentional attack against people who had jailbroken phones, why did it only affect those who used that particular flavor of unlock software?
With a jailbreak being simply a software modification, when has strictly a jailbreak (not an unlock) led to a bricked phone? At worst, a software update from Apple will just lead to the phone being restored back to non-jailbroken state.
it is also legal for Apple to push a change that happens to break jailbroken phones
Are you sure? That sounds like trespass to chattels to me, or if they hadn't tested their update on jailbroken phones, then reckless, possibly criminal negligence.
The second problem is that lawyers will be trying to find a way to create the old result, and are likely to succeed. For instance Apple's restrictions against jailbreaking are almost certainly in their shrinkwrap license contract. Therefore the fact that they can't throw the copyright book at you, doesn't mean that you're necessarily legally in the clear to do it.