Perhaps you weren't aware, but you can click on the Downloads tab (see the image below), at Gamezebo, and all you'll see are downloadable games.
Gamezebo page Gamezebo isn't "concentrating" on Facebook or iPhone games. They just added those categories and there just happen to be a lot more of them released, on a daily basis.
Think about it...if you don't see much in the way of new downloadable games at Alawar, Awem, BigFish, GameHouse, GamersGate, GOG, MumboJumbo, Playrix, WildTangent, etc., Gamezebo can't very well post about things that don't exist.
They've also (a couple days ago) added to/enhanced their Search function so it's a lot easier to find information. See this article:
Gamezebo releases new search features making it easier to find and discover gamesHappy gaming!