Also, we don't have great public transit through high-traffic areas from where people are to where they want to go, because we've got this weird kind of medium density continuous sprawl. There just aren't that many of the good high-density locations at which to place Metro stops, although that seems to be changing more because people go "Hey, let's get a stop here, and then we'll /become/ a destination location."
Also, I don't know of any city I've been in where the "Buses suck, subway rocks" relationship isn't true. I don't think it's just a "buses for poor people" thing, but I don't know what's going on to cause this anecdotally widely observed phenomenon.
Taking the Bus + Train from SF to LA area takes longer than driving, and has more stress. Can I stop to use the bathroom, or will I miss the bus? Not an issue if I am the driver. I realize that's not the same as city driving issues, though.
http://en.wikipedia.org/wiki/Orange_Line_(Los_Angeles_Metro)
They run on dedicated right-of-way. Not just their own lane, but their own road. Not as nice as a subway, but approaching it.