I feel that this idea is somewhat antiquated now. In limited, if you want to maximize your statistical advantage, there are times when it is reasonable to run 41 cards. Case in point: let's say that after drafting, you use math and/or computers to determine that there should be 56% nonlands and 44% lands in your deck. Running 17 lands provides a 42.5% land percentage, whereas 18 gives 45%. Running 18 lands in a 41 card deck, however, gives you 43.9%.
Obviously this needs to be tempered with the overall consistency of your deck. If you deck is more reliant on drawing your 1 or 2 bombs, sticking with 40 is probably your best bet.
A good point. It also doesn't address why 60 cards was chosen in the first place. I agree that with a 60 card minimum, the correct number to run is 60. But why was 60 chosen in the first place? It could have easily been a different number was my point from the beginning.