William's passion and exuberance (never irrational, though) comes through in the hyperbole of his title. But I think his points are good ones and I had one of my own:
Part of his point about removing barriers to entry is that it may be advantageous to install tools in small increments, increasing functionality over time with plugins, than to start with an enormous all-in-one package. Commercial, proprietary software leans toward the enormous all-in-one package for the same reason that restaurants like to serve oversized portions: they can get more of your money at once and achieve economies of scale. But in an uncertain environment, the all-in-one package may be overkill.
Our current environment is uncertain because of the economy (we don't know whether our businesses will expand or contract) and because of the rush of technological change. Open source may be appealing because you can build on it as you go along.