Microsoft didn't delegate in the first place. What MS did is allow those device developers high-level access to the kernel where before they were put in userland where they couldn't do much damage. Once Microsoft decided to do that, their business model is what killed them, although it is now less of a problem because all drivers must be signed (and supposedly tested). Apple also gives privileged access to drivers, but Apple controls the hardware and drivers, making it less of a problem.
What does kind of free kernel access does Apple provide?
In my perfect world, NOBODY would give any drivers kernel access. Take RIM's upcoming tablet that will run QNX, which is an extremely stable microkernel system. Device drivers (including video and network) run in userland, and can be killed and restarted if they become unstable or crash without affecting the rest of the system.
-In my perfect world, NOBODY would give any drivers kernel access.-
That would certainly increase reliability. But I wonder
if such a model would be appropriate for primary storage and video. Some sort of DMA access would still be needed
for these devices to function at acceptable speed.