Well depending on the "trick" I would say the dog has to have a level of obedience, so I don't think it would be mutually exclusive. It would depend on what you are referring too. I guess I would describe a trick as something that doesn't have a real world application, its just for fun. But that doesn't mean its separated from obedience.
I guess my question is, is obedience more being able command your dog (like recalling 100% of the time) where as tricks are the actual action or is it more of heel, recall, and watch me are classified as obedience while sit, walk backwards, and fetch are tricks?
bte2 could probably answer your questions way better as he is a working dog trainer.
I believe obedience is definitely a couple of those things you mentioned, I guess my definition of obedience is your dog tuned into you and listening to all commands and ignoring any type of distraction. I think there are levels of obedience, what might work for a pet owner would be completely different from a working dog owner.
Take for instance walking backwards, for a pet owner it could be construed as a "trick", but a police dog might need to do that in a real world application. I guess it all depends. lol. Personally I love training anything, because it keeps his mind stimulated. We are always trying new things.
As for OB.. different sports require different OB exercises.
For instance AKC trick title considers a retrieve a trick exercise
While, IPG (Schuzthund) the dumbbell retrieve is considered a OB exercise
I kind of consider all tricks OB, it's just outside the general OB you see (sit, down, heel, out, stand, etc..)