Count Zero said:
Starfleet ranks follow American Naval tradition
But American naval tradition follows British naval tradition. The rank structure for the U.S. Navy is (or at least appears to be - I am going by the names of the various ranks since I have little direct experience) nearly identical to that of the Royal Navy...and of course Starfleet ranks are a bit different from both.
But I agree that the show does tend to be Americentric. On the one hand, I think this is a shame - Earth is surely a lot more interesting than it appears to be on Trek

- but on the the other hand, maybe we got off lucky because when TPTB have tried to portray non-American or non-British Isles humans, they don't usually do a very good job.
I mean, think of the many terrible fake accents we've heard on Trek! For that matter, they weren't even very good at American accents, or non-Oxfordian accents from Britain (with Chief O'Brien being a notable exception). DeForrest Kelley was
from Georgia so he could surely do a good Southern U.S. accent, but when they had McCoy do his Southern gentleman accent, it was ridiculously fake sounding.
As for examples, I agree that almost all the main human characters are American. I always that that was weird, actually. I wonder...I wonder if this was done not just because the writers have an American bias but because they feared making a silly cultural error?