Most of his 5 reasons don't hold water: I worked at Martin Marietta, a big defense contractor and one of the predecessors of Lockheed Martin, 1986 - 1992. By 1989, Martin was a total Mac shop, it was very hard to get a genuine PC in the place. That shoots all of his objections in the head, except maybe "Macs don't support themselves".
In the late 80s, Macs basically did support themselves. And that's were the real issue comes in. Companies that had IT departments would have totally been able to get rid of the traditional IT department. Martin had CDC (ugh)) mainframes, which were certified to run Multi-Level Secure, so their IT department was able to ignore Macs, and concentrate on making money and keeping headcount by supporting CDC and their mainframes (ugh). Anyone else, the IT department could see the axe falling if Macs came in.
MS-DOS, PCs and Windows hit this weird window: just enough of a headache to justify an IT department, just enough functionality that a user revolt could be quelled, or at least kept to a simmer.