g-cpan -i "Image::Magick" simply installs media-gfx/imagemagick, but does not confirm that one is building imagemagick with "perl" USE flag enabled. It just happily reinstalls the package, leading hasty users like me to believe that we now have Image::Magick installed.
It looks like +perl was the default in previous versions of media-gfx/imagemagick, but this is no longer the case.