The wording on the site is bad. That is supposed to represent 35.9% of the sites that are hosted are using Linux. Linux is considered a sub-category of Unix on w3techs.

See also: http://w3techs.com/technologies/details/os-unix/all/all

45.2% of UNIX web servers are of an "unknown" variant? How can you detect "UNIX" but not be able to have any idea of what UNIX it is? I'm going to hazard a guess that you'd be able to get numbers of similar accuracy by inspecting /dev/random.

Edit: poking around the site a bit more, I notice that they count Darwin under UNIX but OS X is a separate top-level category alongside Windows and UNIX (albeit one with less than 0.1% share). WTF are they doing? This makes no sense.

Technically you could run a non-OS X Darwin. Maybe that's the explanation?

Could be, but it still doesn't make sense. It's the same underlying stuff, so either they're both UNIX (what I'd vote for) or neither is.

I never said it made sense ;-)

I didn't mean to implicate you in this. I just checked out the site and had to share how ridiculous it is.