The UE4 demo has sh*t art design, while the game caps show exceptional art design. Therein lies the problem of comparing the two. Until either PC, PS4, or Xbox Infinite release big AAA visionary blockbusters using UE4, there can be no legit 'This Gen vs Next Gen' graphics comparisons. Although seeing that demo in motion might help out these early discussions a bit.
The funny thing is that these tech demo screenshots are likely far better than anything we will ever see in the first few waves on next gen games. If people are disappointed in these then when they see launch PS4/720 games they will cry.
Look at the original UE3 tech demo that used gears of war tech. Honestly even towards the end of this generation a lot of games are struggling to compete with it. EDIT: For anyone wondering what I mean by the early UE3 demo here it is http://www.youtube.com/watch?v=1m7T5ay_8DI Unfortunately I can't find a direct feed HD version. However this tech demo was the year before the 360 came out (much like UE4). Look at some of the lighting, shadows cast in it, the detail on textures up closer (like the walls etc). So likewise with the UE4 demo I really don't think we will even see launch titles look that good.
People often forget that there is rarely a HUGE bump between the launch titles on next gen consoles and high quality titles on last gen ones.
Compare a late life xbox game like Black with perfect dark zero or resistance. Conkers reloaded with Kameo. The bouncer with FF9 etc etc. Yes those games look better but it isn't a HUGE difference. In fact with the PS2 to PS3 gen we were lucky as suddenly having games in HD made a big difference. Generally we only see the real big differences once we start to hit the second wave/big AAA titles after a year or so. The PS3 and 360 both getting uncharted and gears almost exactly a year after release.