here is one of the best answers I have found, that to Gravsports.com :
Example: In 1992 I became convinced that good climbers were strong climbers, hence I needed to be strong. After spending months in the weight room I could do a one-arm pull up with 25 pounds in the other hand and many other stunts that definitely made me very strong. My climbing improved perhaps a letter grade or two, which was positive. I then went to France, where I won several pull-up contests, often by miles. Some of these climbers were pathetic, barely able to do ten pull-ups, and these were the best in the world! Then I noticed that I was getting my ass kicked in the competitions, finishing low in the field despite being stronger than most anyone there. At the crags the French were climbing much harder routes onsight than I was capable of climbing with a lot of falls. Something was not right. One night in a bar a top euro climber was expounding on why the French were so good: "We have the best rock in the world. We climb more than anyone else. And we have the best wine." In one sentence he restructured my entire world view of climbing: To become a better climber you simply must climb more. A week later I watched Francois LeGrande onsight a route harder than anything I had ever climbed. Francois had never touched a weight, but god could he move. I resolved to learn how to move. After six months of doing nothing but climbing and studying climbing movement, I onsighted a route harder than anything I’d ever redpointed. So forget weights, strength, supplements, learn how to move and your body will develop the strength necessary for the movements.
Comments from Will Gadd at gravsports.com