Conceivably those few might have included some critical applications, except for the second factor, which I offer in all seriousness: Windows is so notoriously unreliable that no one would ever build a life-or-death system around it.
The Register (Scotland) says:
See also the recent virus infection in the onboard computers of the Eurofighter.
The Royal Navy's plan to fit most of its fleet with command systems based on Windows boxes continues, with the commencement last week of a programme intended to replace the existing commandware of the Service's Type 23 frigates. The Type 23s will make up the majority of the British surface fleet for the foreseeable future.
According to the Ministry of Defence (MoD), HMS Montrose has now entered a planned docking and refit period during which BAE Systems plc will replace her original DNA(1) gear with DNA(2), said to be "based on the system being fitted to the Royal Navy's powerful new Type 45 Destroyers". This means it will be based on fairly everyday hardware running legacy Windows OSes - people who have worked on these programmes inform us that both Win2k and XP will be in use across the fleet.