Billy Idol
Legend
AFAIK they were all demoed on a single 680gtx and that's the reason why I think despite running on the same hardware, C2 wasn't nearly as impressive as the rest. Also using Gears3 vs UE3's initial demo, it's probably not that farfetched to say the actual games using UE4 or Agni would look mostly the same as the engine demo, maybe even better throughout the life time. We're not talking about Nvidia New Dawn demo which it takes sli 670gtx to reach 30fps+, UE4 and Agni are actually quite representative to the upcoming nextgen games according to the devs themselves.
But I think you really cannot compare those two. C3 is an actual game, showing actual gameplay of a game shipping in near future. The gameplay sequence showed a rather big area with lots of paths and ways of playing through the section and interaction, whereas the demos are just demos, nothing more.
Furthermore, C3 is a multiplatform release, as pointed out by L.Scofield, console definitively hold back the whole graphic fidelity...
I would be happy, if next gen graphics have anything to do with C3 on ultra settings at 1080p60Hz with proper AA