Okay, so this thread's about a million years old, but I'm resurrecting it to say I was wrong.
Or, well. Maybe.
Tonight I was talking to somebody about this movie, and brought up (among other things) the whole "graduating Kirk straight to captain" nonsense that I mentioned in one of my rants here. The person on the other side of the conversation said something that stopped me dead in my tracks. I made her go back and explain it, and then again cause I'm dumb. She walked me through it, and I'm gonna try to explain it here, but I can't promise I'll get all the details right.
Here's what she said:
As a cadet, Kirk was actually a commissioned officer with the grade of midshipman. Midshipmen are outranked by all other officers, including warrant officers, but they're commissioned officers, and they're part of the chain of command.
So when he was aboard the Enterprise en route to Vulcan, Kirk's legal status was not in question. Although he was administratively grounded and shouldn't have been allowed aboard, the fact is he was aboard, and his grade made him part of the chain of command regardless of his administrative status in the Academy. (This would not have been true if he'd been subject to whatever Starfleet uses as its equivalent of the UCMJ. If Kirk had been under arrest at the time, it would have been a different story altogether.)
Now, just before Pike shuttled over to the Narada, he gave command of the Enterprise to Spock — verbally, but explicitly — and gave him his orders. In the same conversation, he promoted Kirk to first officer. That's the word he used: "I'm promoting you to first officer." What he meant was, "I'm assigning you to the billet of first officer, which by virtue of your low rank must come with a brevet jump-step combat promotion" to some higher rank, presumably commander. Though he didn't get it approved by anybody, and it wasn't done in writing or anything, this was a legal promotion.
The way my friend explained it, combat promotions are not uncommon these days among the enlisted ranks. Historically, they've been applied to enlisted men and officers alike. Jump-step promotions — where you go up more than one grade — are extremely rare, but not unprecedented. And it's also not unheard of for a promotion to be brevetted — that is, for the promoted officer to assume the privileges and duties of that grade before officially being promoted.
Anyway, point being, four different things happened in that scene, all of them legal under historical military tradition. Kirk was assigned to a staff position, he was given a combat promotion to the appropriate grade for an officer in that position, that promotion happened to skip over as many as eight grades, and Kirk was brevetted, so he could assume his duties immediately rather than having to wait until all that stuff could be formalized.
Stretching the bounds of plausibility? Yeah, big time. But in a crisis situation aboard a ship manned by trainees … I dunno. Seems to me it's not entirely insane. Maybe just mostly insane.
Anyway, here's the important part. Once promoted, a military officer cannot be demoted without due process. If we assume Pike was within his legal authority to promote Kirk in the first place — he wouldn't have been in the real world — then the only way his grade could have been reduced to something below commander is via court martial (or non-judicial punishment).
Once the crisis was over, Starfleet had themselves a whole lot of vacancies in the ranks, and a kid with demonstrated leadership abilities and the permanent rank of commander. It wasn't much of a jump, then, for them to bump him one grade to captain and send him off to make mischief.
I asked my friend if anything like that could ever happen in real life, and she said, "Could it happen? Like, is there any absolute law against it? No." But then she started rambling on about statutory minimum time in grade and promotion boards and my eyes totally glazed over. (Lawyer. Whaddya gonna do.)
So based on that flimsiest of justifications, I hereby officially withdraw my gripe about that one part of the movie. It stretches credulity to the absolute breaking point, but from what I got schooled on tonight, it at least makes a sort of sense.
(And yes, if that was Orci and Kurtzman's intent, which I don't believe for a second, then they could have at least mentioned it in passing somehow. But I can't figure out how to explain all that crap without stopping the story dead to do three pages of dialogue about Starfleet law. So in the spirit of Christmas I'll even give 'em a pass for burying the sense under a bunch of lens flares and explosions.)