They are saying that over time, compression of the foam in the pads slowly changes the sound. Which is true, however it's incredibly slow, incremental and undetectable while it's occuring. Almost certainly, a well worn 5 year old pad is going to sound different from a new pad to the trained ear. But that's just pad wear, not burn in. Of course, brain burn in is simply the brain getting accustomed to the dynamic profile of a set of cans. OP is simply trying to rename pad wear and is suggesting that this is what people experience when they experience headphone "burn in" of the drivers.