That seems silly, sellers are in all kinds of different situations that could prevent them from sending docs back. After my 4 resales I've learned to be more patient with the resale/closing process--I was the holdup my last resale and transferred funds a day after the seller returned their docs).
It's interesting hearing these differing opinions because it's the complete opposite for me. It's more stressful having money just sitting there in escrow (not earning interest) whether it's a couple days or a couple weeks.