General purpose operating systems are beaten hands down by single use firmware, nothing particularly new there.
A telephone system I had which we only recently stopped using was bought in 1997, but the system design actually went back before that to the days where DOS was the mainstream operating system. In its service life it'd seen Windows 3.1, NT, 95 ,98, ME 2K, XP, Vista, 7 & 8 come and go and it outlasted all of them. It was ditched because we wanted to migrate off of it before BT discontinued the type of telephone line it used on our exchange; that's the sort of lifetime that a well put together tech product can deliver.
If it'd have been running on any general purpose operating system then it'd have had to go decades ago.