The reality is that if you poke yourself out of the Mac & laptop world, there's plenty of desktop computers without integrated Bluetooth support, and Bluetooth

The reality is that if you poke yourself out of the Mac & laptop world, there's plenty of desktop computers without integrated Bluetooth support, and Bluetooth <-> USB adapters are pretty cheap, so vendors usually ship with one bundled to ensure they don't have to deal with tech support issues from people thinking they have Bluetooth support in their computer when they don't.