Import of pdf differs from ghostscript results . . . whay?

hi,

I take a CMYK PDf file and convert this into a tiff file using  
PerlMagick = ImageMagick.
If I do the same only whith ghostscript I get another, much better  
result in Colors.

Especially the BLACK channel is preserved using GS.
IM is removing all Black . . .

You can download an Archive (3MB) from here: http://www.ademmler.de/ 
files/testfiles.zip
test4C.pdf	= source file
im-out.tiff 	= ImageMagick result
gs-out.tiff 	= Ghostscript result

Hints are more than welcome, thanks.
Alexander