You're partially right, but only in a very broad sense. One of the really ugly problems with web search is identifying real content from meaningless crap, and wikipedia rather nicely gets rid of nearly all the extraneous stuff, or boxes it in.

The actual semantics stuff is pretty robust, but like any piece of software can be tuned to get incrementally better results on any corpus.

Really, one of the major reasons we started with Wikipedia is that we wanted to build out the core search infrastructure and website infrastructure. These are non-trivial things to do while also setting up a search interface thats suitable for public consumption. I'm sure you can find a longtime powerlabs user to tell you how far we went in the interface and speed department.