The bit about "Teams building new supervisors or other system-heart software will of course need machines of their own. Such systems will need operators and a system programmer or two who keeps the standard support on the machine current and serviceable." sounds funny if you are making desktop software - but for big ecommerce systems I think that it still holds true. The class of software that folks were working on 30 years ago were big centralized, always on, money making, "enterprise" systems.

I would update the rule for today and say the following: If you are working today on an online banking website, or a banks trading system, or anything else, putting in a well managed staging environment, that mirrors the live environment, between the developers and production environment will save you a lot of pain over the life of the system. Getting management to sign off on the extra kit can be hard. Getting management to buy into the "delays" that are caused by the developers not having root access to this kit is harder (i.e. has its own system administrator that is not in the development team). In the long run having such an environment there and under strict change management reduces downtime when you are dealing with large, bespoke, online, money making systems.