It's not so much "improved" valve seats, it's more that the valve seats are hardened steel pressed into aluminum heads. Even a slight overheat will expand or distort the aluminum and BAM! the valve seat drops. I would imagine even without an overheat issue, over enough time (200k+ miles) the heads would probably distort enough also.

I have a 4.7 rebuild thread in the Jeep section which shows the catastrophic results of a dropped valve seat...