Orci said that the alternate reality used in this movie is a departure from all the other time-travel rationales in previous Trek.
I don't consider this a big deal. I just think of it this way:
It's the black hole. That alone makes this different from any previously seen method of Trek time travel.
Assuming that this is not just an alternate timeline, but an alternate *universe*, that the Narada
and the Jellyfish
both crossed into. (It would certainly explain a few things, such as the look of the Kelvin
, the differing stardate system, etc.)
Thus, the prime timeline we all know and love is doubly protected.