Well, I'll agree with the OP;all that white is blinding on the default on large TVs, even with toned down/calibrated settings. It also usually also makes the plasmas buzz in agony.
Even with the dark skins, the default webpages STILL have a stark white background. I had to change those also to go along with a dark skin.
If it is ever "blinding" then your display is certainly not properly calibrated. And if it's a plasma, it should be even less "blinding" since they dim the screen the brighter the image gets.
An all-white screen will typically be less than half the brightness of a small white window on a plasma display.
I really don't see this as a Media Center problem, since pretty much every other program on your computer will behave similarly, with white backgrounds everywhere.
If your plasma is buzzing when your computer shows an all white (255,255,255) image, it is set incorrectly (or busted). They only do that when they are showing white out of gamut (higher than 100% white).
My Panasonic does NOT do this.
I've had plenty of plasmas that do this, from many brands.
If your Panasonic is a commercial panel, perhaps that is an exception because they often use more robust power supplies and less aggressive ABL. Or if it's an older model with a fan running I suppose that may mask it.
There are a number of other reasons why buzzing may or may not be an audible problem with plasmas and high APL images. (position in the room, wall mounted, where you are seated etc.)
I won't go as far as saying that all plasmas do it, but all plasmas I have ever been in contact with have.
Regardless, this is not indicative of a fault, or necessarily of doing something wrong - though I'd definitely recommend checking that the input/output levels are correct.