That's not exactly the reason. By design, common cards are supposed to be the weakest. So, any common quick zero cost card that doesn't hurt you is, as EricH says, an absolute no-brainer to take. It's basically a "draw again", with a chance to get an uncommon when you would have got a common. Even a zero cost quick card that does absolutely nothing would be overpowered (not overpowered in the sense of being a game-winning card, but in the sense of being a card that you should always logically include in your deck).