While true, the term of author using his power to resolve situation in his writing is called "deus ex machina" and is generally considered bad writing. Author is SUPPOSED to make story hold even without himself.
Yes, such simplified case makes possible to show what can happen in clear way. I also saw it somewhere ... oh, right, it's on wikipedia explaining casual loop.
You can model cases like this even with the billiard ball. Also remember that quantum physics is principally statistically based and when multiple outcomes are possible, which one happen is random, so it doesn't need to be ONLY possible scenario, just likely enough - and the fact that time travel happens isn't, by itself, something which would lower the likehood of scenario happening.
I believe it does justify existence of such loops, although it's harder to explain why exactly was everything in superposition in advance ... it's because existence of time travel itself makes the scenario when time travel WONT happen LESS stable than the scenario with stable time loop, because someone would try to interfere. In the Gargoyle case (note that I didn't saw that episode), someone ELSE would try to travel into past but failed to form a stable loop, while the character itself going into past does result in stable loop, so it can happen. In terminator case, later episodes (which allowed past to change, but anyway) established that sky.NET is something which can happen even without time travel ; presumably, it would then invent time travel and try to change the past, failing to form a stable loop. Similarly, the resistance would try to change the past. It is possible that the stable loop that happened, which DID bring sky.NET faster BUT also gave resistance their leader, is the most likely stable scenario from all which could happen - and it actually makes sense, because both sides trying to utilize time travel gained something. It's even possible that it solves the major problem with the movie, specifically the fact that it would be easier to send into past something which would wipe out whole city: it's possible it didn't happened BECAUSE it didn't resulted in stable time loop. (Although the explanation that authors didn't think it though is easier.)
... also, it's not MY quantum-physic based explanation. I would like to take credit but I suspect that I didn't formed it independently but only based on story which explained parts of Novikov self-consistency principle ... and, in fact, had I remembered how it's called, I might just refer to it instead of trying to explain it myself.