There are no "linux web frameworks" either, aside from Rails I guess, because I don't know of any currently popular language other than Ruby that doesn't really work on Windows.
Most frameworks are obviously not bound to a particular OS but almost all of them are developed on a Unix and more or less assume a POSIX platform.
Yes, many do have a section in the docs for "Installation under windows" but that's normally intended for a development environment, at most and comes with many little strings attached such as "not tested on windows"-markers in the docs and raised eyebrows on the mailing list.
