Morphology to me is equivalent to binary morphology for a long time since the begin of my graduate study. I never met/thought about grayscale morphology before. Until recently, I read some papers about low depth of field image segmentation, and the grayscale morphological operations together with high order local variance computation is used very often for segmentation. My thought about morphology has been refreshed.

http://www.ph.tn.tudelft.nl/Courses/FIP/noframes/fip-Morpholo.html#Heading104
http://www.leptonica.com/grayscale-morphology.html