The converse is that if they scored first, you believe there's a goo chance that they can go on to win. How long is it since we felt like that. Under Moyes about 15/16 years ago probably. That's a long time of being a nervous wreck.
I said this on twitter the other day. I havent seen tmhe stats, but I can't remember the last time we lost a lead in the last 25 minutes of games. We've barely lost a lead at all (think that United game at home where we have a mad 15 minutes in the 1st half). So you can't really say it hasn't or doesn't work. He probably plays the odds too, and knows, worst case scenario we will end up with a draw.
You even think of games like Leeds, where they threw everything at us for 15-20 minutes after half time, but after that we were quite comfortable. I'm convince we were probably 2 or 3 minutes from getting a win against Leicester too.
Whatever they do in the final 20, whether it shape, or superior fitness, or whether we are just good at last ditch defending I don't think, but there's something in it for sure.
I don't know about anyone else, but in honesty the clock seems to win down very quickly for me in the last 15 minutes of games.