Why only 10-bit depth dng files from 16-bit Nikon D90 nef files?

Question

When I convert 16-bit .nef files from my Nikon D90 to DNG I get only 10-bits depth.
Since the camera should be producing 12-bit depth it seems I am losing information in the conversion, and I don't want that.
I have installed the 7.1 DNG converter, and I suppose that is what is used when I download from camera memory card through Bridge 5.1 and click dng conversion.
Same thing if I open the .nef in Photoshop 5.1 , which kicks up CameraRaw converter 6.7.0.339.
Why is this?
Can't .dng have more than 10-bit depth?
Sverk

Answer 1

Well, according to the user manual and to the review in
http://www.imaging-resource.com/PRODS/D90/D90A.HTM
the D90 delivers 12-bit color depth in the .NEF files.
Of course, I haven't looked at the actual pixel data to find out how finely graded they are.
What I'm looking at is what Bridge 5.1 (WindowsXP) says about the files in the
Metadata/ Bit depth entry. 
In that, the .NEF files are listed as "16-bit" depth (although it will actually hold only 12-bit resolution), but when converted to .DNG it says only  "10-bit",
and that holds both when the conversion is done automatically during the importing from the camera, and when converting from .nef files afterwards.
Archiving pictures in the .dng format seems to be a good idea -- but only if no information is lost in the conversion.
Thus, the "10-bit" info showing in Bridge worries me.
Might it be that the meaning of bit depth is different in the two file formats?
Might there be something about the de-mosaicing that necessarily consumes two bits of depth?   Whether in the .dng conversion -- or when saved .nef files are later to be used?
In other words, for practical purposes, are the formats equivalent in color resolution,
Or is there indeed a certain loss?
Maybe a very difficult question, but I'd sure want to have a technical ly definite answer before I dare switch to using the .DNG format all the way.
Sverk