>If that were true bodybuilders would do great at marathons and triathlons.

It takes more than leg and back muscle to do great at marathons and triathlons. Aerobic development, VO2 max, lactate threshold are just as important. Further, you would want less weight (muscle mass) in the areas that are not required for your marathon. That's why many professional bikers and marathon runners intentionally neglect gaining upper body muscle.

Weight lifting won't train you to run a marathon, but it certainly isn't detrimental towards multi-hour hikes. Don't move the goal-posts on me :)