Look at the chain and think carefully about it's workings.
Lecap, not to start an argument, because you are partly right, about the chain needing lube between the rollers and the bush, but I must strongly disagree with you on the part where you reckon there is very little wear between the sprocket teeth and the roller.
The area between the sprocket teeth and the roller is important to lubricate, what do you think wears your sprocket teeth other than wear between the teeth and roller?