Say we decide to end support for a piece of hardware today. What does this really mean?
It means we stop selling it.
It specifically does not mean that we yank it out of the field immediately. Customers running this hardware still get some time before that hardware is out of warranty and their replacement cycle occurs. During that time, they're still full-fledged customers; they get support and upgrades just like everyone else.
So dev still has to worry about the hardware, at least as much as they've ever had to (translation: most of the software isn't hardware-specific). And QA still has to certify new releases, patches, etc. on that hardware.
Stopping support for something doesn't mean no longer worrying about it. Stopping support for something merely starts a timer that means sometime in the future we won't have to worry about it.