Digital BW, The Print

I recently bought a Nikon D70 and am having lots of fun taking photos of my son and 
printing them on an Epson 1200 with MIS VM inks.  (My 1200 is especially well calibrated 
to the VM curves because it was the "model" that Paul Roark used to generate the curves 
for this printer.)  One thing I've noticed from prints from this 6 megapixel DSLR is that, 
unlike MIS VM prints I've done from scans of 6 cm x 9 cm color slides converted to black 
and white in Photoshoip, certain shadow detail areas (especially my son's hair) end up 
having large pixelation blocks (areas where there are large blotchy blocks of black ink).  I 
notice these types of areas on prints larger than 8 x 10" (i.e. printed a 180 dpi) and to a 
much lesser extent on some 8 x 10" prints (i.e. printed at 240 dpi).  I've noticed this from 
other digital cameras, in particular my Canon G2.  My hypotheses as to what's causing this 
is that: a. It is caused by the Bayer pattern, and/or b. It's caused by my overaggressive use 
of the levels and/or curves commands in Photoshop to get a full range of shadow values.  
It's not just in the prints but also noticeable at 100% view in Photoshop, although much 
less visible in Photoshop than in the actual prints.  Has anyone else noticed this 
phenomenon?  Any decent solutions for getting rid of it?  BTW, my work flow is to shoot in 
raw, and use the Photoshop Camera Raw plug in.  I work entirely in 16 bit.  I am very 
skilled in Photoshop.  I do not oversharpen.  Thanks for your help.  BTW, I love the D70.  
I'm falling in love with photography all over again.