The problem is that iMessage simply attaches to regular SMS and takes over that,
No, that's not true. iPhones will happily send and receive SMS messages all day long for anyone that chooses not to manually activate the iMessage feature.
there isn't a service you stop using per se because people still always simply messaged you using your phone number which is what SMS uses and what iMessage ends up taking over.
Apple has no control over users that attempt to send iMessages to former users of the service.
So when you are not using it anymore the takeover should be done and simply regular SMS would be used with people still using the same old phone number they always used for you, whether you had iMessage or not. That's where the difference is and that's where the issue lies. All these other analogies are simply not the same because they don't have one service using the same identifier as another service as is the case for iMessage simply using your phone number as SMS does and selecting which one should be used on its own based on what Apple servers say.
Apple is free and clear on this whole process because iMessage is an "opt-in" feature. The functionality described in the lawsuit is a result of users specifically choosing to use it, thus they shouldn't be surprised when it stops working after one side of the conversation decides to stop using the feature.