I too used to think like you do. But I've been using Ubuntu at work, and now when I go on a Mac I actually miss the usability features of Ubuntu.

Just a tiny example: hitting alt and clicking anywhere on a window to move it instead of going to that top bar. Or the multiple different ways to switch between apps. etc. etc. There's probably 100 small things that I now can't live without. So I would say the statement "Mac Os X is not as usable as Ubuntu" is actually true. Surprisingly.