ImageMagick handles "raw" images (such as Nikon's NEF format) using "ufraw-batch" for delegate.
The delegate is invoked to convert the image into a temporary file (in ppm16), which is then further processed by IM.
Unfortunately, the EXIF information is lost during this transition. Although ufraw can transfer EXIF data from source to output, it can only do this, if the output's format is JPEG.
Not sure, how to best address this problem -- maybe, IM ought to read the EXIF data from the original "raw" file, and the actual image -- from the ufraw-produced temporary ppm16 version?