Sshowing what an engine running a demo of it's best features is a bit different from a game with AI, players, small levels to fit lowest common denominator platforms, etc. We always see these terrific engine demos, but rarely anything like that in actual games where a whole lot of other stuff has to go on as well..
Having said that, Cryengine have always shown the most impressive visuals, and with the editor built into the game, it looks like an amazing platform for developing on.
I'm guessing the only reason Unreal Engine seems to be more popular is pricing and support from Epic.