There was a small developer that took the opposite approach with Cities XL back in 2009 (when Nehalem showed up with quad-core CPUs). Monte Cristo.
A pretty looking city simulator game. Single threaded, and had a nasty memory leak problem. And it didn't restrict the size of your city like SimCity 2013 does.
Cities XL can bog down even on a 5 GHz i5 when your city's population starts to reach beyond a hundred thousand due to every commuter's traffic pathfinding, a very similar issue that the older SimCity 4 DE has (especially when Network Addon Mod is used on SC4, which makes the traffic pathfinding more realistic and unlocks many additional transportation network construction options... At a large CPU hit though).
And that's assuming the memory leak didn't cause the game to lag horribly enough to force an application restart, or crash.
The new developer, Focus Home Interactive, only added new cosmetic things over the course of four years, but neglected the single-core support issue and the memory leak.
Edited by A Bad Day - 6/28/13 at 8:03pm