I haven't noticed that on my 4R, as it only has 30k miles on it so far, but I would imagine a seat is like a mattress, you can only get so many year/miles out of them before they go bad. From my experience, it is the softer seats, like the ones I had on my Grand Cherokee's, that pack out faster. With the 4R seats being a bit on the firmer side, I would imagine they would last longer. But at 100k+ miles, I can imagine they are not as comfortable as they day it was driven off the lot.