Well jailbreaking is also breaking digital locks. As for the copyright thing, yes, they could ask the user to upload the ipsw (but still i don't see the differ

Well jailbreaking is also breaking digital locks. As for the copyright thing, yes, they could ask the user to upload the ipsw (but still i don't see the difference between user doing it and them doing it, it'll end up in the same place), but there would be no need for modification instructions. Modifications are done dynamically, they're not pre-applied into a custom ipsw.