I am guilty of lurking as well.
You could lable it voyerism, but most of the time I just don't have a need to argue or show how intelligent I am. Which I are not.
Plus, if I were to make a shitload of responses just to have an impressive post count I wouldn't be helping the community here. Time will take care of my post count, and experience gained from the board will allow me to help someone in the future.
What was that old poem again? About the "wise old bird"? The less he spoke, the more he heard.
If you spend most of your time broadcasting you have little time receiving.
This is my only defense.