Some people are very sensitive to fit items, like crank arm length. Some are just highly influenced by what they're told. Some times you can't know which you're dealing with as a fitter (untill a long term relationship is developed, like a doctor).

I know i like a crank size much more then the other possible sizes from years of trying the others (doesn't matter to the public which it is). All my bikes have this size reguardless of the bike's purpose. Andy.