The midfield helps a lot with the defensive work, it's a swarm defense that they play, which is fine if your players have the fitness levels to do it. Like I said, we did that in the first season, all over teams. In the Premier League obviously you will find more athletes and quick players, so Liverpool's is an even more extreme example of that.
For instance Glen Johnson is a crap defender, I know that as I've watched him for years for Liverpool and England, but you don't often see him exposed anymore. He's an athlete, and Liverpool have a good mix of ability with their athleticism.