Well, that's only the "mobile" Unreal 3. The same engine games on iOS and Android are using. It's not really the "same" Unreal 3 we see used in Devil May Cry 4 and other recent PC games based on it. It's probably a scaled down version even of the original Unreal 3, not the "Samaritan" one.
They probably couldn't have done more even if they wanted to, though, since asm.js or not, browsers can see only use the OpenGL ES 2.0-based WebGL API's. That's why I'm hoping the OpenGL ES 3.0-based (or better) WebGL will arrive very soon, although I haven't even heard if the Khronos group is working on it, so it's possibly they haven't even started yet.
This is the full Unreal Engine 3, all 1 million + lines of C++ code.
The art assets of the Citadel demo are I believe the same as in the Flash demo, which were optimized for a more mobile-friendly and touch-friendly environment.
However we also showed a full Unreal Tournament demo running, as I mentioned in another comment, both at our GDC presentation and in the booth where people could play it. That's a full desktop level.
They probably couldn't have done more even if they wanted to, though, since asm.js or not, browsers can see only use the OpenGL ES 2.0-based WebGL API's. That's why I'm hoping the OpenGL ES 3.0-based (or better) WebGL will arrive very soon, although I haven't even heard if the Khronos group is working on it, so it's possibly they haven't even started yet.