Digital BW, The Print

When, under diffuse lighting, I look at a sheet of matte black ink on matte
paper next to a sheet of photo black ink on "photo" paper, the latter simply
looks more black - despite your "valleys and hills" argument.  As a result,
I conclude that the photo ink/paper combo is better at absorbing light
(ignoring specular highlights for the moment - see below) and that the
measured dMax difference we observe between matte and photo is largely real
despite the argument that the matte paper is likely to reflect a little more
light back to a 0/45 degree sensor because of its more diffuse reflection.
The issue with photo paper is that it is more prone to specular reflection.
This is a big DISadvantage.  I am sure that if photo only produced the same
black (visual or measured) as matte then matte would rule the day.  I would
argue that matte paper has been the choice du jour for inkjet only because
of issues such as "bronzing" and "differential gloss".  These have largely
been dealt with by the new K3 inks.  The next step is a paper with a finish
more closely resembling the air dried fibre print.  Personally I like the
finish of matte papers and if one could achieve a photo dMax on matte then I
would do all matte.   I suspect though that that day is still a wee way off.
Photo ink/paper just took a massive leap forward.  I don't see such gains in
matte ink/paper.