Pages' full-screen mode is relatively new -- as far as I'm aware, it wasn't added until the Lion update. Scrivener et. al. have had the market to themselves up until now.

That being said, the fullscreen mode in Pages actually seems like a pretty nice compromise between features and non-distraction. Apple's obviously been taking some notes. :)

Not sure when it was introduced, but I know I had it with iWork 2009 on Snow Leopard.

Only runs on Mac, only runs on Mac, and only runs on Mac.

In the context of this article, "only runs on Mac" is just fine, as Write Room also "only runs on Mac."