I think this pretty clearly defines the what is and is not wilderness:
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Sorry, I couldn't resist.   :)

If you look at each exterme, non-wilderness is where there are lots of people and things are highly altered by the presence of those people.  

On the other end, pure wilderness would have no people, and no one to even look and say "hey, that wilderness over there."  It might even be nearly impossible to access.  This would also mean that no one would know or care about that wilderness, except in a philosophical sense, since they'd never been there or seen it.

I think of the BW/Q as "accessible near-wilderness."  "Accessible" because many people can get to it if desired.  Not pure but "near" in this sense: if left alone for a fairly short period of time (a generation or so), it would largely seem to be pure wilderness to a new visitor (until they find the occasional concrete dam, logging artifacts or cabin remains, etc.)
-Tom