He didn't include one of the most essential knots to tie two ropes together: the one-sided overhand bend (http://en.wikipedia.org/wiki/One-sided_overhand_bend). It's very strong and really simple (which is most important in stressful situations when you can't afford any mistakes).

In rock climbing when you do multiple pitches, you usually climb with two ropes (50 or 60 meter each). That provides double safety and you can abseil 60 meters straight. At abseiling you make the bend on one end, put the rope through the carabiner on top of the route and use both ropes to get down on. Then you simply pull on one rope and both come down.