Last season, Barcelona depended on the following players: Valdés, Adriano, Alves, Abidal, Piqué, Puyol, Mascherano, Busquets, Xavi, Iniesta, Keita, Pedro, Messi, Villa.
That's 14 players. Pep Guardiola had lots of luck with injuries, because that means you're four players away from starting a reserve player.
To the 2010/11 group, Barcelona added: Cesc, Alexis and Thiago. That makes it 17 men who are very reliable starters.
In other words, Guardiola almost has two full starting teams at his disposal this season.
Right now there's three starters injured: Piqué, Alexis and Iniesta. Thanks to Barça's depth this year, nobody's worried as they still have 14 top-level players to fill in without dropping performance.
On the Madrid side of things, they have their 11 starters: Casillas, Ramos, Pepe, Carvalho, Marcelo, Xabi, Khedira, Di Maria, Özil, CR7 and Benzema. But after those it just drops off talent-wise, and it's difficult to find replacements that guarantee the same level of performance on the pitch.
Coentrao is one. Arbeloa is another. That makes it 13. What about the rest?
Higuaín seems to be a different player since his back injury (much like Kaká), while the rest are simply reserve players that are there for emergencies.
It's no wonder Mourinho fields the same XI almost all season long. But a couple of injuries or fitness problems could impact Madrid severely this season.