I'm speculating here, but from my experience with Windows powered oscilloscopes: Windows is on the measurement device, it's not a networked or USB controlled peripheral with a documented network protocol connected to a standalone PC. When you open up "Device Manager" you'll see a bunch of specialized USB and PCI/PCIe peripherals that make up the actual measurement function and user-interface.
So the company selling the spectrum analyzer would have to publish quite a lot of their internal documentation regarding hardware registers for the data acquisition boards, and they'll be reluctant to do this: Much of a modern measurement equipment's functionality is inside the data processing, and by documenting the interfaces it would make it possible/easier to reverse-engineer or extent (without paying for options) the functionality.
If the buyers were to stick together and only buy from suppliers who allow access to modify and redistribute the source code of these devices, perhaps they could create incentives for the devices to function with newer software.
Why would the navy pay for support if the computers on xp were airgapped? The only reasonable conclusion is that these computers are on the network accessible from outside.
Consider that the US was able to attack air-gapped computers in Iran and destroy industrial equipment. Air gaps can be breached, it's just a little harder.
So the company selling the spectrum analyzer would have to publish quite a lot of their internal documentation regarding hardware registers for the data acquisition boards, and they'll be reluctant to do this: Much of a modern measurement equipment's functionality is inside the data processing, and by documenting the interfaces it would make it possible/easier to reverse-engineer or extent (without paying for options) the functionality.