Well, I would agree with some of what you say, but any control system utilising PCs or not will be obsolete at some point.
If we didn't buy a computerised control system because the components will be obsolete in the future, we wouldn't be able to buy anything.
The project manager(s) at the time buying the latest available system doesn't make them idiots, as far as I can tell.
(I haven't been responsible for buying any of our systems, in case you were wondering).
Anything we use to make our products requires revalidation if 'upgraded', from standalone weighing scales to full blown SCADA systems.
Like I said not ideal, but realistically the organisation cannot justify the downtime and huge expense - and the frequency. I'd love it if they could.
None of our control systems have internet connectivity. We are not permitted to use USB sticks.