During the past few weeks, I've encountered a couple of times the statement that there is no difference in the shifting performance across different tiers of Campagnolo rear derailleurs. I.e., one gets top-notch performance even from their cheapest offering. Supposedly, higher-end derailleurs are more expensive due to the lower weight and materials used.
Is there any truth to this? Is there any other difference between a, say, Veloce and Super Record rear derailleur other than price and weight?