Old wives tale (unless you are very overweight and run in sneakers on concrete or something equally stupid) If your joints are going to wear out it is more a factor of lack of exercise (such as running) and genetics than over exercising and/or running. Older peolple who had a poor exercise history and have joint problems, who are put on an exercise program that includes running, tend to see a reduction of those very problems you say running is bad for.
Well...you have to take it on an individual basis since one of the most common ailments associated w/running is "Patellofemoral Pain Syndrome" or commonly known as "runner's knee" where in certain cases, running causes , among other things, cartilage and bone degredation (in addition to knee pain, limited mobility and that yucky "crunching" sound). This is due to the mistracking of the patella (knee cap) which is excacerbated by running.
Mistracking is caused by genetics (being flat footed), improper or lack of excersice (causing uneven development of your quad muscles), or injury. This can be remedied by physical therapy, proper footwear, knee braces or in extreme cases, surgery.
But the bottomline is, running
can be more harmful than beneficial in certain cases. But I agree that barring the above exception, running (or some comparable cardio activity) is a necessity.
*Squeak!*