'Crayford' is not a registered trademark, nor was the design ever patented - scroll down to the bottom of this page:
http://www.observatory.org/featurmr.htm
Yes, they operate smoother than bog-standard R&P's, but R&P
can be manufactured to be smooth and almost backlash-free too... but I suspect that would be more expensive now than mass-producing serviceable crayfords. Some Japanese and German high-end scopes of a few years ago came with good R&P focusers.
There is a third type, which is less common on telescopes: the helical focuser, like the focus ring on a camera lens. I have seen them recently on some ultra-light designs, but they have always had their fans...