I'm pretty sure it's just a placeholder. They're not going to reuse one garish bit of old content in the game when they've totally redesigned everything else from the ground up.
I actually found out a little more about the e3 demo. It was an actual demo format that the engine was then playing back: meaning that all the action was "sampled" at a fairly low rate, and then interpolated: giving it a bit of the sorts of hitchy prediction artifacts (like inexact relative timing of various events) that multiplayer games sometimes have. An actual running game doesn't have such problems (though they are pretty hard to see) but Valve decided that the demo playback system was good enough for the purposes of wowing people at e3. This comment was edited on May 21, 19:46.