Because Apple specific hardware is not AVAILABLE on the PC platform. Because it is TIED to the APPLE OS/Hardware. You cannot even plug it in to the PC half the time. It is DESIGNED to work with Apple at a very core level for timing purposes/low latiency. And every time Apple upgrades its OS, it no longer works. Once a year it no longer works. And Apple then tells these companies to deal with it.
This reminds me of the PC gaming industry years ago: for performance reasons, the game developers bypassed as much of the OS graphics hardware abstraction as they could. They would then get bit by every OS release as Microsoft made changes to the underlying graphics APIs. And everyone blamed Microsoft.
Another example: Microsoft and Intel data show that roughly 80%+ of the blue screens of death in Windows were when the hardware hung during a BIOS call. In other words, while you were not running the Windows OS. Again, Microsoft was blamed. Hence why they are a big supporter of EFI.
And as a final note: I bet Apple doesn't tell them "deal with it", I bet Apple suggests they "use the proper abstraction layers and APIs" to help abstract them from under the hood changes in OSX releases.