And hopefully, self driving cars and quadcopters and other drone robots can use a 3d model of a city, to better navigate the real world. How about teaching a self driving car, with the GTA 6 - Your City game?
Or you can use osmosis to cut a file down to any arbitrary area: https://wiki.openstreetmap.org/wiki/Osmosis
SuperTuxKart is a free, open-source racing game. This page is about generating 3D levels for the game, using OpenStreetMap data.
Then again, for common elevation data, there are loads of other good sources which can be used in conjunction with OSM, not sure about licensing though.
granted, this is probably more on the "intellectual property" and "secret sauce" side of things.
How do they figure out the building heights at all then?
I think the data was found here
I don't know how this software does it, but people are tagging "number of floors" for buildings, and you can get a decent estimate of building heights from that (by presume X metres per floor). When standing on the street, you can easily figure out the number of floors.
This is not legal advice.
Copyright is different, in the sense that in the absence of a license, the default terms in the law actually prohibit one from copying stuff, hence one can't claim ignorance.
For example, would a texture used in a game that has a environment grid generated from the osm database be considered an adaptation of the osm database? I personally don't think so, on the concept that the concept of databases has conceptual borders which generally don't include textures.