The public transport congestion is reduced by higher density. Pretty much everyone (in Sydney) is trying to get to the center. If you have more dwellings in the center, you reduce the number of people relying on PT. In cities that are less of a star structure, this may work even better. People end up trying to live close to their workplace and relying less on the transportation.

The need for transportation is a side-effect of not having sufficient dwellings close to where people are commuting to.