In terms of how it's properly pronounced it's always been OS Ten from the start. Nobody from Apple has ever stood on the stage at a keynote that I've ever viewed and called it OS EX. I can't understand why anyone that's been in tune with Apple's products would purposely call it OS EX? And from my experience I hear this more from people that live in the UK than anywhere else and frankly it's sickening and irritating.
It has always been the Macintosh Operating System with a version number using a roman numeral 10 (X). How could it be anything else? It was System 7, OS 8, OS 9.....why would it be OS (EX)?