this is my opinon on this. feed them in the tank.
you may noticed that when you take them out of the tank thay are less likly to eat because they were just handled kinda the same reason that when you get a snake you let it settle in for a bit before trying to feed.

if you handle (returning it to its cage) any snake after it just ate you run the risk of being bitten by a snake still in feed mode or it may reguge.

I maybe wrong on this but the people that say if you feed in the cage that they associate their tank with feeding. I DON't belive that a snake is smart enuff to make that connection.