PHP actually seems like a good balance in terms of server support vs. (what I can guess of) the application requirements. It's brain-dead simple to run and if you weren't precomputing everything a page needs for response-time reasons the language would push you towards doing so anyways.

I wouldn't be surprised if they're using PHP for what it was originally meant to do (add a thin layer of dynamic-ness to straight html) and precomputing all of the data it uses in something else.