That is actually funny. I also saw the same thing, wanted to return a set top box coz I had two and they said if I return it at Verizon store, it will cost 9.90, but I can get a free shipping box sent to my home.
I believe the reason is to charge for that many more days while the packet is in transit.
They might even take 1 month to send the return boxes but I wont be able to contest.
I think the reason they started charging is because once someone returns a box to a store it becomes part of that stores inventory and gets put in a closet with every other one. When I got my new dvr at my store the closet they pulled mine from was very full. I bet they want to prevent to much store inventory and would rather have the equipment sent to their warehouse. If thats the case why wouldnt they just mail the boxes to the warehouse? Who knows. It is nuts though that they charge at all.