People aren't really concerned about the security of their non-internet connected HVAC controller or elevator. If it's in the wall people don't really think about it or update it.
And in cases where it doesn't have any communication mechanisms with the outside world, telling it its 1990 again in 20 years isn't going to be a problem.
Yah the time on the thermostat will be wrong, but if no one has upgraded it in that long, its probably ok, put a piece of tape over it.
Mostly embedded, industrial systems, medical devices, set-top boxes and home routers. You connect to the serial port or gain access by other means and most of the time you are greeted by ancient versions. It gives me the chills.