Originally Posted by koffee brown
That's a big yes, though the best weight bearing exercise is strength training with weights.
Another thing to consider from studies with regards to running and osteoperosis- though runners do protect themselves from osteoperosis by using running as an impact bearing activity, they still tend to get osteoperosis in the upper body, since the impact doesn't affect the upper body- only the legs. So you'll still have to do some weightlifting for the upper body to prevent osteoperosis in the upper limbs.
Koffee
What about big hill workouts, or an intense fixed gear ride? A rider must come pretty close to the weight bearing effect of running but without the jarring on the joints. I agree that the upper body is in need of some kind of workout whether you are riding or running.