The question of whether or not to grease BB threads or not isn't critical for most people. However for those who ride in the rain it can easily become critical. Dry threads tend to wick and trap water leading to corrosion problems. Keep in mind that water doesn't always enter from the outside. It often enters at the seat tube and dribbles down into the BB where it stays a while doing it's damage unseen.

BITD as a Campy service tech I'd often get severely corrosion damaged BB cups. Customers weren't happy when I showed them that the cause was within the BB and not water that was entering from the outside.