Most companies use Word for their documents, which doesn't lend itself too well to the standard version control scheme since it's a binary file.

Then there's the whole open source thing that certain companies are afraid of (not worth going into or arguing about, but it's there). Some places do use Sharepoint, which will do versioning on Office files, even though it sucks, but it does cost a lot more!

Ultimately though I prefer writing documents in a wiki, though I might look at something like Github for that now too.