As far as I can tell, that's only true in fairly unique situations, though, in the super-cities. I live in a decently sized city (metro population of perhaps 3 million people, around 25th in the US I believe) with a transit system mostly regarded as 'pretty good' (but no subway, just light rail and buses) and it would be rare even at rush hour for a car not to be faster. Usually signficantly so.

I think what it comes down to is that if you have a subway system, that will probably beat cars, in the limited area it serves. Once you have to do transfers to buses, it gets much slower. In the places I've visited with subway systems (SF, DC primarily) this is definitely the case.