I had no idea that any such game has so much Python code. I was under the impression that Python (and Ruby) were too slow for most game stuff. very cool.
The UI for Civ 4 is in python. You can modify it to your hearts' content. (I hacked it to communicate with Dragon NaturallySpeaking so the UI would be voice accessible.)
You can write game logic in pretty much any language on modern hardware. The only things that need a highly performant language are the 3D graphics engine and geometry, and any deeply nested AI computational stuff. Your standard game logic of object movement, collisions, physics, is orders of magnitude less demanding than that.
Games are no exception to the standard rule of software, that 95% of the time is spent in 5% of the code. You can use whatever language for the other 95% and not see any meaningful problem with performance.
