Someone asked earlier so I thought I'd give the scoop.
Edit: I started writing this post and it got too long so I decided to leave the long part last for whoever cares and the short answer first.
BTB/WTW is a color range used mainly by Consoles & PCs (I should say they can be set-up to use it, its not mandatory). They are ranges in color that aren't used in broadcast TV or movies (DVD/BD Discs). If the TV (or the AVR) isn't able to display BTB/WTW information, it basically 'crushes' black/white detail (by making several different shades of black just look the same shade, vice versa for white). The best way to test this is to use a calibration disc (AVIA, DVE, etc) with a BTB pattern and see if it is displayed properly.
BTB/WTW (Blacker than Black / Whiter than White):
The standard range for Movies (DVD/BD Discs)/TV Signals is from an RGB scale of 16-235 (give or take 1 unit, I can't remember). You'll notice, that the range begins at 16, which means there are 15 more ranges available at the bottom end. The same is true at the top end of the range, it goes up to 255 (although, not as obvious).
These ranges (0-16, 235-255) were initially used for synching a video signal but today are not really required. Problem is, since our whole TV system was built around this range, old sets weren't made to go below 16 or above 235, hence, if you started making it a standard today, many people would not be able to see a proper image on their existing sets.
Now, a lot of CE companies are providing BTB/WTW support in their products since there is now a significant audience for its use. Will this become a standard eventually? No idea, but I wouldn't hold my breath as it wouldn't be anytime soon.
Please correct me if I was off in anything...