Ever taken a CD rom drive appart?
*watches reaction*
Well the motor is generaly not connected directly to the tray these days, they used to be connected by a gearing system, nowadays they are connected by a rubber belt..
So older drives suffer from pushing and pulling (come on, admit we've all pulled somtimes)..
Newer drives don't suffer as much, there's still risk but it's reduced..
I put my finger though the CD's center hole and push the button, not only does it save my motor it also keeps me on my toes..