As a rock climber I must agree that a knife is a necessity. As Scouter pointed out some good reasons to carry one.
When I first started climbing, I really didn't care to carry a knife as I figured it would get damaged. That changed when I was doing a short climb, I was leading and on a very hairy edge which if I moved much I would fall. My protection was not very solid, so I really didn't care to take a fall, my only choice was to keep climbing. Unfortunately a piece of rockclimbing eguipment that I was carrying wedged in a rock. Being that I was on a very small edge, trying to yank the thing out would have caused me to fall, luckily I did have a BM Auto Pardue which cut the webbing from my sling allowing me to climb on.
The morale is that a knife can be handy just about anywhere, I know I don't go anywhere without mine.
I feel a CRKT Bear Claw will do a person just fine for rockclimbing and rappelling needs. It has a curved blade like the Anso and doen't cost as much, about $25.00 to be more exact, which is exactly the price of a knife I don't mind damaging in such hostile enviroments like climbing.