If I remember correctly, Far Cry had a foliage generating program so that no two trees were exactly the same. It sounds very similar to what you speak of, I've thought of this before too, basically a program would describe how a building/environment is supposed to look and then design it itself. Its probably the future of gaming really, as graphics get even more out of control and people demand more cars (it could be used to generate cars too), cities, etc, development time would take so long that somethings gotta give, and generating all those in-between not particularly noticable buildings (see also: tedious work) would speed up dev-time, and landmarks can be done by people if they really want them in the game that badly (which Rockstar would)
Just think: this could also be used to generate interiors to buildings, a very tedious thing to design. Every building could be enterable!!!
Good point, I didn't even think of a program that could do the same work. Though one drawback is the city may seem soul-less, having one generalized idea behind everything. Of course, they could go back and edit this stuff later to make it seem more like a lived in city