The Web is a formidable tool to host documentation; nothing new about that.
But documentation, be it on the Web or not, tend to rot when not maintained. Nothing new about that either.
While documentation maintenance is probably better addressed at the social-engineering level, there are tools that can help manage it; namely, a few weeks ago, W3C Systems Team went through the process of cleaning up our internal documentation on processes, tools, services, configurations, etc. that sits on our Team-only Web site, but is too rarely kept up to date with the latest developments.