I was under the impresion the reason it was called OSX was that one of steve jobs previous positions before coming back to apple,
Was at a company that was running an operating system called neXt that was unix based.
The way it is spelled was the logo ie neXt hense the X
10 was the number of the OS,
so all revisions of the OS come back to the old apple way ie 10.1 10.2 and so on.
apart from running a small animation team that he funded and set up which consisted of 4 people in the begining 11 years ago and has grown a little bit and is now known as Pixar ,
which is why steve jobs is now on the disney board.
Busy man.
Mind you apple do make great machines and i have one lol.