It's the profile that forces the printer to use all the inks to create a composite black/grey. And it's the rendering intent which shuffles it away from actually being a good composite black/grey. Trying to get a neutral greyscale out of composite inks from an inkjet printer is the photographer's nirvana - that's why photographic inks are available in three or four shades of grey (such as Epson K3, or the Lyson Quad-black). In the relatively tiny gamut of dye-sub ink, it's a tough task to get even remotely close.
I had a design to print on lots of mugs awhile back which featured a photo on the front and black/white on the back. I actually ran the paper through the printer twice (once using the profile to get the colour photo, and then again using no profile and "greyscale" to get the b&w). Results were far better than sending it through once and ending up with a composite black/grey.
The next question will be - is Sawgrass black ink actually black? Well...
