I interchange OS X and OS10 when speaking. Fact of the matter is that you don't know how it's 'supposed' to be pronounced unless you've heard somebody say it, and there are no instructions on pronunciation on the box.
I also think most are smart enough to realise that X is the Roman numeral for 10, and that versions of the Mac OS existed before this, regardless of how they say it.
I also think most are smart enough to realise that X is the Roman numeral for 10, and that versions of the Mac OS existed before this, regardless of how they say it.