Check our injury list:
Buffon, Grygera, Zebina, Knezevic, Andrade, Tiago, Poulsen, Camoranesi, Nedved, Iaquinta, Trezeguet.
At least 5 starters are injured and 6 more bench players. And Ranieri can still make a strong starting XI.
That's squad depth for you. Instead of investing in one or two superstars we invested in 7-8 good players.
We have both RB's injured and we still have Salihamidzic and Mellberg for RB. We can have both LBs injured and we can still put Chiellini or Salihamidzic to play there. With 3 of our Cbs injured we can put Grygera and the 4th CB in the center of the defense. We have many CMs, we have Salihamidzic and Giovinco for MR if both Camo and Marco are injured. We have De Ceglie and Giovinco, even Brazzo, if Nedved's injured and we have more than enough strikers.
Look at Milan on the other hand. They have no squad depth but they have more quality players. With only three players injured (Nesta, Gattuso and Kaka) they are dead.
I'm not saying that it's better investing in quantity than quality, but as it turns out at this particular moment, we did good when we decided to get Tiago, Grygera, Mellberg, Iaquinta, Salihamidzic and De Ceglie instead of buying only Ronaldinho.
Of course, this was a good thing to do last summer. Now when we have the required depth, we must go for quality, top quality.