Abrams recast Kirk, Spock, McCoy and the rest, and told the origin again for a new audience. The interesting part is the mechanism. Rather than declaring the older films void, the 2009 film writes a time-travel incursion that splits the timeline, so both continuities stay canon and the original is left undisturbed. Leonard Nimoy plays the original Spock inside the new film to make the join explicit: a remake that argues, in story, that it is not replacing anything.
