OS X is technically correct, but it's 202M hits on Google for OS X vs 82M for OSX. As far as I'm concerned both are widely used by technical and non-technical people and mean the same thing. It's a tiny mistake that could be fixed in one second, why are we even mentioning it in the context of Isaacson allegedly blewing the biography?
A Google search is hardly the way to resolve that. OS X searches for anything with OS or X whereas OSX only searches for things with OSX so of course the former has more hits.
I mean you're right that it's technically "OS X", but your methodology for proof is flawed.