Back to the chain question: let's see if I've got this right. My LBS was explaining that the width of the chain has to do with the number of gears. Like I have Campy 10 spd, if I had a chain/deraileur for a 9 spd it might be too wide. So as deraileurs get more and more gears as in converting an old 10 speed to modern bits there are conflicts.

Could that had been what the LBS meant? He could replace the chain but it would have to be a new chain of the right width.