If you mean web companies and software companies, then yes, there is quite a bit of Ubuntu. Very occasionally you'll see Debian or even something like Gentoo. Non-technology companies tend to stick to Red Hat 5 or 6, at least here in the U.S.
It's easy to forget when you work in software, but software is not a very large part of the overall economy. Sectors like oil, bulk chemicals, healthcare, and so on completely dwarf software and those guys have computers too.
So if you love monocultures, come over and work on enterprise software! You'll also get the fun of dealing with 5-year old system software and its bugs. RHEL 5 is very much alive in the enterprise space.