That is the descriptivist viewpoint, yes. However, descriptivism is not the only valid point of view. Prescriptivists (including me) would hold that decimate means to reduce by 10% because *that's what it means* from both its literal etymology and original usage. However, dictionaries are written by descriptivists, because if you purchase one prescriptivist dictionary you're pretty much set for the next few centuries and that's not the ideal outcome for publishers. Additionally, descriptivism has been used as an excuse for giving existing words new denotations while preserving their existing connotations, a common and highly effective political tactic made even more effective by descriptivist education's message that the practice is both acceptable and admirable. With the pursuers of both money and power on their side, descriptivists probably assume their ideas are the only ones that matter, but they're as wrong about that as they are about the language.
Decimate: To reduce by one tenth.
Biting the hand that feeds IT
