Why are three dice better than one?

I used to play a lot of D&D back in high school and for a few years after, first edition AD&D to be exact. I also used to read comics, and made some friends through the comic shop I used to go to. My buddy Mike, who plays in the game I'm running now, had been playing D&D with some other guys from the shop and found fourth edition Champions to play a super hero game with. Myself and another friend Dave played in some supers games for a while with Mike as GM. I really liked the way the game played, with the Hero System's touted ability to create any character you could think of. Combat rocked, with lots of options for hand to hand and powers to do just about anything. And the 3d6 used for actions was a lot different.

In the meantime Mike had gotten some other books for Champs/Hero, one of which was Fantasy Hero for 4th ed. "You mean we can play fantasy with these rules too?! My mage can have a sword if he wants, and my fighter can do a whole lot more than 'I hit him with my sword!' ? Well sign me up."

I haven't rolled a d20 since.

Hence, three dice are better than one. Not meant as a slam on anyone's preference's, but it's catchy I guess, right?