I think I'm gonna do this upgrade to my articulateds just as preventative maintenance. Not that I'm having an issue with the stock shafts but these steel shafts are 100 times stronger. I like my stuff bullet proof. Just pop it on the track and go. I doubt these shafts will ever fall apart.
Only reason I can think that the factory shafts were nylon is cost. Perhaps for quiet operation as well. Nylon doesn't need a shot of grease every now and then.