Why did PSG deserve to win? They kept missing chances, you gotta score to win. Not to mention they were fortunate on both of their goals last week. Barca's defense does need work, though. Even with Puyol/Mascherano healthy they weren't playing great defense, now that they have to play Adriano, or Bartra if Adriano is seriously hurt, it's going to be even worse.
Really, though, just goes to show how damn good Messi is.