So you're post prompted me to look, and I see that P90X does use a pull-up bar. I have to imagine, however, that it was simply a decision regarding equipment. Much easier for people to get by with one or 2 sets of dumbells. Plus, for the people who can't even do one pull-up, they can do rows and curls with a light dumbbell. Nevertheless, I can see how no pull-ups would be a drawback for people that are already moderately fit.