LOL
Try Cisco IOS and real UNIX.
Yes, anything critical runs on “real” UNIX, like AIX. (I sure hope you don’t mean SCO UNIX.)
But for most small to medium size webservers (that make up a significant majority of the Net), Linux is their first choice. (That and Apache, MySQL, and PHP.)
Yes, I know the Net has move beyond LAMP now, but enough of it still exists to call it “classic.”