I believe it is realtime too. The red horizontal beams in one of the shots look crap enough for realtime gfx, but everything else just looks crazy crazy good. Of course, much of it comes from the insane texture and geometry detail level of those models, and the lighting is fabulous, and there's probably uber post-processing going on too.
Those shots are very clean, but there is some aliasing in a few places which leads me to believe they may actually be realtime. If so, they've massively improved their lighting model.
Currently the retail shops are showing a price of $60 for the Xbox360 version. I imagine that puts the PC version around $50. So ... Does anyone know if the game is only Portal and Portal Co-Op, and won't come in a bundle like The Orange Box with HL2/Ep1/Ep2/TF2/Portal? For me, if it's only Portal single and multi-player, the Xbox360 version won't be worth it until it drops down to $30, and around $25 for the PC version.
Both the "Meet the ____" and the L4D videos are stored in compressed streaming video format, however I really doubt they were actually offline rendered. They look perfectly compatible with in-game graphics and what we can expect from realtime source engine graphics, just with higher-res buffers for smoother shadows and antialiasing.