It bugs me a bit too, but I guess there's nothing really wrong with it being "the exception that proves the rule" - something extraordinary happened in that case, unlikely to repeat.
And the pre-existing time travel rules weren't exactly clear-cut, either - my original response glossed over bootstrap paradoxes like "Time's Arrow", where the characters travel back in time because they found Data's head in San Francisco, which was only there due to said time travel.
But then, from the perspective of people in the future, I suppose all time travel events look like bootstrap paradoxes...

Oh cool, GFR has finally gone mask-off.
This has always been the case, but I'm going to take this opportunity to state that links to that site are not allowed here, and will be removed on sight.