That jab/cross combo you speak of were arm punches used to score and keep Leban off balance and unless your chin is glass they won't hurt, but rather annoy you.
Silva put the meat on his shots following a high left kick and a quick move to his left to set up the four punch combo that put Leben down. And, like Sell did witih Smith, Leban came at Silva with his CHIN UP. I don't care if you have a chin of granite if you get caught right, you will be hurt or knocked out.
Look at Smith's technique when he threw the punch. It had all his weight behind it and he turned it over well at the very end of the shot getting his shoulder and hips into it like he's supposed to and it caught Sell right on the point of his chin (the KO SWEET SPOT). Yes, every chin can be dented as it's not a matter of who hits harder but rather the technique being used as I've seen far too many greats have it happen to them to think otherwise.
And these were guys with GREAT chins, which I still believe they posses this day though I've seen them hurt or KOed before.