Using engine braking to slow the car doubles the number of times the throwout bearing has to carry a load, and it also places a heavy opposing load on the drivetrain parts. Lots of automatics do a good job of using engine braking, but they don't do it with the severity of the average manual transmission user who is practicing downshifting for engine braking.
Another thing I would like to point out while speaking of clutch wear is about sitting at a traffic light. Some people will sit at the light with their foot on the clutch for the entire cycle of the light. This will significantly reduce the life of your throwout bearing.