Blogger John Will down in Australia had a good point about rank in a recent post:
“Getting a black belt is easy – becoming a black belt is something else entirely…”
Our coach is fond of saying that rank isn’t given, it’s earned. And it’s something that I agree with: a student has to prove they have progressed far enough, and has worked their way into the next rank. Which should also explain why everyone’s time at certain belts so greatly varies. Everyone’s journey is different: circumstances change, people change, techniques are learned at different paces- there shouldn’t be one set, standard schedule for a time at a belt. It takes as long as it needs to take, essentially.
Granted, some instructors are “more strict” when recognizing students and their advancement in rank. Conversely, some rank is recognized in what would be considered a ridiculously short amount of time. And the cold hard truth is sometimes rank really is “given” for reasons other than the student’s skill and progress. No one is perfect, and neither is the system. The biggest thing you have control of in this whole process is yourself and your advancement. Keep with your training, continue to drill, train, learn- because regardless of rank, no one can give, or take that progress and knowledge from you.
A Skirt on the Mat 
Over on Fenom’s site, Triin was saying that Ashton Kutcher got his purple and folks all over the internet lost their minds. http://poweredbyshe.com/2015/01/16/the-green-eyed-monster-of-belt-envy/
I also have the same answer about grades as your professor: “Grades are EARNED, not GIVEN.” My students all the time will either complain about why I “gave” them the grade they got, or thank me for “giving” them the grade. Each time I redirect it and say “Grades are based on math, not feelings.” Jiu jitsu strikes me the same way.