That's one example, another one is for smaller assets - trees and vegetation, for example (SpeedTree). There's definitely a market for creating 3rd party tooling to help with developing a game. There's actually quite a few companies and technologies that specialize in one aspect of a game or game's world.

There's a few other interesting technologies that add a lot of content to a game for relatively small investments; think physics and destruction engines, animation technology (iirc there is something developed by EA's sports games branch that can generate intermediate animations for smooth animation transitions), world generation (height maps), etc.