Too lazy to RTFA, I take the meaning of the summary this way:
Like a society can be judged by how it treats its elderly, infirm, and more fragile members, a coding project (open source or privately funded) can be judged by how it treats its least well regarded developer.
Are you Nazi Germany, do you show people the door based on the color of their eyes/hair, how tall they are, their GRE scores, or how they perform on some arbitrary admission test before you give a 15 minute in-person interview?
Are you Genghis Khan's Mongolia, do you abuse and then fire anyone who isn't running at the front of the pack? Rank and yank does not generally improve morale.
Are you the European Middle Ages, do you just ignore your weaker team members and let them be consumed by plague rats / drown in their own stinking code while you isolate the shipping product in the ivory tower?
Are you a more modern quasi-socialist society where you educate your weaker team members as best you can and enable them to contribute as they are capable?
There are cases to be made for the advantages and efficiencies of all approaches, but, generally, you need to be a strong development team to carry and build up the weaker team members - if everybody is too focused on product and producing to care about helping their fellow team members to improve, your team is overtaxed (too weak for the job at hand) and probably not able to perform well (provide a reliable living wage for the developers while producing and maintaining the product) in the long term.