The two Manc clubs have had virtually injury free years (with regard to their best players such as Aguero, Rooney etc).
Kin thickos. We've had significant spells without Welbeck, Cleverley, Nani, Valencia, Young, Anderson, both Da Silvas, Smalling, Lindegaard when he was the starting keeper, and oh yeah, we haven't had Vidic since the first week of December, but Rooney's been fine, so that's virtually injury-free there.
That's an entire XI there that probably beats Liverpool's Top side 6 or 7 times out of 10