It's all about the chipset hardware and drivers, which are not standardized across the PC world. Some people don't care about Bluetooth, and they want to pay less for their boards, so manufacturers oblige them. On a PC, you have to pay extra for decent wireless performance. On Apple Macintosh you pay extra always, whether you want it or not, but you get consistent quality in return.

Have you considered the possibility that there might be more than one Bluetooth host adapter manufacturer for Windows laptops/PCs, and in addition to that more than one way to wire up said adapter correctly to ensure good radio propagation?

"Works on my machine" when it comes to Windows hardware is a pretty narrow-minded take.