Supposed crash-proofness of Vista video drivers

At http://galego2.spaces.live.com/Blog/...2A33!186.entry
is the claim, "Unlike the Windows XP display drivers, the Windows Vista
display drivers run in the user mode of the operating system. That means
you can update your drivers without restarting the operating system. It
also means a crash in one of those drivers won't take other things down with
it."

If that's true, then why does Vista sometimes crash (screen goes black,
monitor goes to sleep, ctrl-alt-del does nothing, all hard drive activity
ceases, and num lock and caps lock lights no longer respond on the keyboard)
when I try to play a .wmv file in Media Player?
I haven't even installed any third party video drivers; all that's running
is the stock driver that came with RC1 (build 5600).
Before anybody asks, "What video card are you using?", note that that's
quite beside the point; if Vista video drivers are supposed to be isolated
so that when they crash they don't take down the entire system, then it
shouldn't matter which video card (or even which drivers) I'm using. But for
the record, I'm using a Nvidia 6600GT.
Nothing is overclocked, system stability was solid under XP (even when
playing the .wmv files in question), memtest86 never showed any errors, and
the current OS (Vista RC1) was installed from scratch after wiping the hard
drive, so this has got to be a software problem.
I understand that this is beta software, which means that it still has known
bugs, but isn't the point of Vista's new video driver model to prevent
driver bugs from crashing the entire system? What's the point of the new
driver model if the system is still at the mercy of the video drivers
anyway?
I also realize that maybe the problem isn't with the video drivers at all,
but perhaps with something even further from the hardware, like Media
Player. But then, isn't Media Player supposed to run in user mode too, and
be able to crash without taking down the entire system?