Quote: Stable kernel ABIs benefit everyone. Suppose I sell an expensive piece of specialised hardware, and provide drivers for it, and then go bankrupt because I can't make a living selling to such a small niche. If the kernel ABI is stable, your drivers If not, you or someone else will have to hack them up and rebuild them.
First off, in reality there is no such thing as a stable kernel ABI in any mainstream operating system out there.
When XP64 was released and people upgraded (I was one of them) there was a great shortage of 64-bit drivers for existing hardware devices, making lots of them unuseable for XP64. When Vista was released with a new driver system lots of hardware which was fully functioning under XP was suddenly unuseable under Vista, because the hardware companies have no incentive to support legacy hardware, they want to sell you new hardware.
So in your example, your hardware wouldn't have survived either the transition from XP to XP64, or XP to Vista. And not to Windows 7 either which by default requires drivers to be signed.
Had you instead open sourced your driver it could have been ported to all the above, and had you submitted it for inclusion to the Linux kernel it would have been maintained by the kernel devs and kept functioning across any kernel abi/api changes.