As a long time B&W shooter with film, (but strictly digital these days), I'm of the opinion that the look and appeal of many B&W images (especially those from using film and going through the complete wet process from start to print), is extremely subjective. Even if 10 B&W shooters are given the same negative shot on a given film stock and then told to print it up....you'd end up with 10 very different looking prints. Sometimes the differences would be extreme. Throw in this mix, the same image shot on 10 diffferent kinds of film stock and have each of those 10 photographers print up each of the images, you's have 100 different looking interpretations...some similar, some different and some as extremely different as one can imagine.
Same thing with taking a color digital file and handing it out for conversion to B&W and then printed (or shown on the web). With color, generally there is more of a narrow range for interpretation. Yes, there are some differences, but a red car will always be interpreted as some hue of red. Same as the blue sky. Hues, contrast as such may be adjusted differently but all the images generally will have more in common than "said" B&W images I cited as an example and outlined above. It may be B&W, but I've seen the same image printed so differently, that some tones of a given piece of the image ran the gamut from deep deep gray, to very light grey and everything in-between. Color filters on the lens enhanced these differences even greater.
I think what is a bit lost with looking at files from the MM vs. say the M9 or other color digital cameras, is the advanatges of the MM files as related to a wide variety of B&W looks when compared to these other color digital cameras. Kristian outlined in words, some of the differences he has found. Since the MM, like any color digital camera files converted to B&W, it generally has to have its output worked on in post processing to achieve some sort of reasonable "look", so looking at files directly out of the MM, really doesn't indicate much with regards to a final product. Additionally, I beleive a more true comparison of MM files vs. M9, would have to be where very similar images of a subject, is taken with both cameras at the same time and then this pair of files given to a number of photographers, instructed to adjust, so the output of the pair of files from a given photographer is as simlar as possible but at the same time adjusted to their own particular interpretation.
This is where the photographer comes in...no different than the choice film based photographers have to make, not only with paper stocks and chemicals for the print, but their choice in film. All I can think of is "subjectivity" comes to mind and if an image is successful to most peoples "eyes", aside from the actual subject matter, people will let it be known and graviate towards it. Again this is not dogma, just my own personal belief.