In this specific case, there are mitigations available that do not require installation of software, but merely a configuration change. Also in this specific case, the people who run IT at NHS are completely incompetent, and this has been well-documented for several years.
In the general case, "I have a lot of machines" is an excuse provided by the unable to evade being held responsible by the uninformed.
The phone company used to have (they still might, I'm not in the business anymore) large labs that were small replications of their network. I've been in meetings where the goal was to decide if we should try to get our latest release through their process - if yes and we were successful they would pay big for the latest features, but if yes and it failed [I can't remember, I think we had to pay them for test time, but the contract was complex]. A lot of time was spent looking at every known bug to decide if it was important.
That's what you get when you defund critical services.
Again, the problem is that rolling out patches quickly often leads to unplanned problems that can't be easily detected or rolled back from. That can cause problems worse than leaving security issues unpatched.
The business of cybercrime is changing. With the growing popularity of ransomware, we should expect a gradual decrease in time between a published remote vulnerability and your systems getting attacked. It may be useful to delay patches by a day to see if there aren't any glaring problems encountered by others - but it's not a reason do leave open holes that were patched in March. Frankly, there was no good reason why this attack hadn't happened a month ago; next time the gap may be much smaller.
Yes, there is a chance that installing a security update to break your systems. But there's also a chance that not installing a security update will break your systems, and that chance, frankly, is much higher.
Furthermore, "That can cause problems worse than leaving security issues unpatched" seems trivially untrue. Every horrible thing that might happen because of a patch broken in a weird way may also happen because of an unpatched security issue. Leaving security issues unpatched can take down all your systems and data, plus also expose confidential information. A MS patch, on the other hand, assuming that it's tested in any way whatsoever, won't do that - at most, it will take down some of your systems, which is bad, but not as bad as e.g. Spain's Telefonica is experiencing right now. What patch could have caused them even worse problems?
You just download the monthly rollup: http://www.catalog.update.microsoft.com/search.aspx?q=401221...
Any competent sysadmin will have these available on their internal update server and push updates+restart during off-peak hours.
Receptionist computers that can open websites with untrusted JavaScript can't reasonably be held to this certification. Certification isn't what kept the NHS from applying patches.
[0] http://www.kraftkennedy.com/block-2-microsoft-patches-preven...
There is such a thing as staged rollouts for this exact type of scenario.
In previous environments I've worked that were "regulated", any change to the environent, such as a firmware upgrade, triggered an entire re-regulation process (testing, paperwork, etc).