Hmmm... Recently, I read an instructional piece on fine tuning. It basically said the same thing that Ben asserts. It was saying that if you had three lenses, at -5, -8, & -14; you could set the default at -5, and then you wouldn't need a setting for the -5 lens, and only a correction of -3, & -9 for the -8 & -14 lenses respectively. I was convinced.
After your post I looked at a couple D7000 books. In my opinion, Digital Darrell is a little wishy washy (or unclear) on the issue. In his opinion, the only reason to use this feature is when your camera or lens is out of warranty. If in warranty, it should be sent to Nikon to be fixed.
David Busch said rather clearly that the default is only for lenses not specifically set in one of the 12 CPU lens settings. I believe this is your view as well.
I would love for the OP to set the default at -20, and then setup his lens for -7. Or he could do it it vice versa, and see what the results are. Personally, I would really like to know before I go through all this falderol.