Digital BW, The Print

I posted this a couple of days ago and got no answer, so here goes 
again. I printed a B&W in RGB without using any curves and it printed 
quite nice (I forgot to apply curve) After appling the MW curve I 
noticed an increase in contrast. It didn't match the monitor but the 
one without the curve matched. Any ideas on why there would be a 
contrast change

Vinny
http://www.wulfsden.com