When it comes to the minor details I just look at it as J.J. saying: "These are Star Trek fans. A lot of them have been engrossed in this stuff their whole lives. They know Khan's details for the most part, so why go into a five-minute soliloquy about the Eugenics Wars and where he's supposed to be from? We have to keep the film's pacing going, and besides - if the folks in the audience want to know more about Khan there are tons of websites, books and DVDs that talk about the guy."
At least we have 46 years' worth of backstory on Khan to inform us whether J.J. went into detail or not. Want a rant about something that should have been explained better onscreen? Picard being cloned in Nemesis.
It's almost as if the screenwriters realized they were just leaving a ton of gaping plotholes and timeline inconsistencies wide open for the nitpicking and took the Seinfeld
route, going "The Romulans wanted to infiltrate Starfleet, so....there's this kinda famous captain they've heard about named Picard....and yadda-yadda-yadda....bald clone who's slowly dying and loves black leather and capes."