A bit of an old thread but I'll poss anyway...
While games, including LFS, do usually have multiple threads created, about 99% of games today only use one thread to do anything meaningful in terms of cpu usage.
In case of LFS for example, there's 11 threads created for me. But if you'll look at the CPU time taken by those threads, you'll see that over 99% of the CPU time is used by only one thread. This one thread does the physics, graphics, sound, input, etc. one after another. With this kind of setup you are not going to get anything useful out of a multi-core/SMP/SMT system for the game alone. While that single thread is, by default, switching between the cores/processors by the windows scheduler it will still never be executing in both cores in parallel because it is only one thread.
For a game to take advantage of multi-core, you'd need to separate major chunks of the game. For example in LFS you could separate the physics code from the graphics code, or handle the physics of each car in their own thread. But coding this to work (well) in a game is rather difficult, especially if the engine was not originally designed with this in mind.