I never said it was a perfect analogy. Only certain elements hold true. You can look at it as either the way I stated it or the highway analogy.
Fast Single Core = Fast traffic on 2 lane highway.
Quad Core = Slow traffic on an 8 lane highway.
At the end of the highway, the same number of cars (or calculations) come through. But if you're in a tight group of cars and can't split up (a single process), the backed up 8 lane highway is rather inconvenient.
Basically, multicores are helping us handle LARGER applications with many "car types" that can split up into the different lanes, but it doesn't help the lonestar process that isn't designed to utilize multiple lanes.