Well obviously that's the real world explanation for it, but from a fictional perspective it is a bit of a continuity error. Don't get me wrong, though. I don't mind as much as I sounded like I did. No need to argue about it.
It's not an error, it just differs from our assumptions. We've never previously seen Starfleet designs of the 2230s, so we have no reason to assume they didn't look like what we saw in the
Kelvin scenes in the movie. And everything after 2233 was in a divergent history, so there's no reason the designers wouldn't have made different choices. If anything, what's erroneous is something like "Mirror, Mirror" or "Yesterday's Enterprise" where somehow the designers in two different timelines make exactly the same design choices in lockstep for decades or centuries, even when designing ships with very different missions in mind. But that's just a conceit arising from the limited budget of television production. Given a fuller budget, I'm sure that the shows would've given us an ISS
Enterprise and a "Yesterday's"
Enterprise-D that were very different in design from their main-timeline counterparts.
Just to play devil's advocate...think about it - why would Kirk's father being killed while Kirk was born have any bearing whatsoever on how Starfleet designs their uniforms and ships?
As Roberto Orci has said in interviews, his take is that Starfleet's analysis of sensor readings of the
Narada after the
Kelvin attack gave them insights into technologies from the future, thus altering the rate of technological progress. Also, in the wake of the attack, Starfleet would've had an incentive to build bigger, more powerful ships as a defense in case the threat returned.
As for the uniforms, see above. Take the same history and run it twice, and the two versions will diverge simply by random variation, chaos theory in practice. There doesn't have to be an obvious, direct causal chain leading to every single change. Especially when dealing with something as arbitrary as fashion. Maybe the Starfleet Quartermaster was in a different mood that day in 2250-something when asked to choose between ugly, drab unisex turtlenecks and bright tunics with a Starfleet arrowhead pattern woven in. Maybe a different designer got hired that year in the new timeline because the designer from the original timeline had moved to a different planet because the Earthman she married in the original timeline had gone to a different college and never met her, because the mentor who'd originally inspired him to go to her college had died aboard the
Kelvin this time around. Every event is influenced by thousands of prior, seemingly unconnected moments and decisions. Change even one thing, and the ripple effects will be pervasive and impossible to predict.
Again, what we've seen in the past is even more implausible -- like the 24th-century uniform designs from Riker's
hallucinatory future in "Future Imperfect" showing up in
real futures or parallel timelines later on. Don't confuse a conceit arising from limited television budgets with a realistic depiction of timeline parallels.