I think if you start young too you build up some strength. When me son was just a year old we would take him to the play place at the mall and he would follow the 3,4,5 etc year old kids up the slide and parents would come over to us amazed at how well he gets around when he had just learned to walk. He went from barely being able to walk to climb anything within a couple week. he's fallen plenty of times but manages to not get hurt as he's built up his muscles pretty tough.
climbing is one of the issues we have with MIL, every time he hears a siren he climbs the back of our couch to look out the window to see the fire trucks and she yells at him for it and we tell her to not yell at him that thats the only way he can see out the window and its our couch, if it was her couch he was climbing on she she didn't want him to it would be different. She wrote my wife a pretty nasty letter just this weekend telling her how he's going to be dead or crippled because we let him climb on things.