Sounds like Vista is using a microkernel architecture. The advantage of this is that if part of the kernel or driver model dies, it can be reloaded without screwing anything up.
Microkernels have been around for decades, but they went out of vogue in the late 70s(?) because they ran slower than a monolithic kernel. They're more robust, though, provided the core kernel is done right (and whatever people might say, MS kernels are generally pretty reasonable; it's the drivers and other crap that usually causes the BSOD) and computers these days are fast enough for the speed/stability tradeoff to be worth the shift to microkernels. This also lets them shift all driver code into Ring 1 and 2, ensuring that Ring 0 doesn't get tainted by anything that might bring down the system.
Microkernels are generally easier to test and debug too, so the quality of the kernel should be higher. And kernel updates can be installed and activated without rebooting, so there should be fewer 'Windows Update needs to reboot your computer' messages. Even Linux can't replace the running kernel in memory without shutting down apps.
