None of the things you mention have the bone density benefits you get from weight lifting. Farmingand forestry involve lifting and moving stuff, sometimes. The point of weight lifting is that it's concentrated strenuous activity focus on a particular body part for short periods of time, if you don't think it's productive, you should look into the long term health benefits of weight lifting. Sure, some machines are just for vanity, but most free weight and barbell excersizes aren't. Weight lifting benefits a farmer and logger by making his farm chores easier and safer. Also, exercise programs are often designed to counter act the muscles that are over developed in their job, for example coders should be doing more back and legs workouts because the position of their job which is chest and shoulders.