That is the only explanation of it. Moleg Bal put some kind of spell on all our character's hair so it never grows one inch longer, but we also can never cut it. Seriously, my sorcerer has had the exact same hair for over a year and a half! It's almost creepy.
Seriously though, what the crap ZoS? A means of at least changing your character's hair style and color is a pretty basic feature to pretty much every MMO, even many RPG's. It was even added in one of the first DLC's for Skyrim for pete's sake!