Orci said that the alternate reality used in this movie is a departure from all the other time-travel rationales in previous Trek.
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.
I like that one the best. It would be nice if Spock had said as much. That while the technology and ship designs were different, enough remained the same time for him to adapt and recognize it, like Scotty and Kirk.