It's not based off of Quake. It's based off of Cube, which, as far as I know, was written from the ground up. The map format is actually very limited and was designed for simplicity -- at least that's how it was in Cube. The author didn't want to spend a whole lot of time on the technology -- just wanted to make something he could actually finish. I haven't tried Cube2, but in Cube, mapping was just a big grid, and you could raise or lower the "cubes" or angle the top of them. That was it. You can do a lot more with quake mapping, so the lack of elaborate maps is the fault of the mappers, not the engine.