Maybe I can explain this phenomenon. When people really ooh and ahh over a mic, it's usually because that particular mic is one that has a certain tone that flatters a certain source in a pleasing way. However, mics that are designed to be neutral don't flatter anything, they just tell it like it is. These mics aren't likely to make a big impression on listeners. But, when it comes to multitracking and layering several instruments, you realize the true value of neutral, accurate mics. If you use a mic that has a strong tonal character on more than one instrument, then it starts to throw off the equalization curve of the entire recording - the whole recording starts to get that particular sound. This is usually not a good thing. But neutral mics use the sound of the particular instruments to yield the different tonal flavors. They impart none themselves. You learn to appreciate this characteristic when it comes to mix-down.
I remember, when I was working in a studio, the SM81 probably got used more than any other mic we had on hand - precisely because of it's neutral tonality. Listening to the raw feed into the control room, they tended to sound very "ho hum" to me - nothing to get excited about. But, everything we recorded with them always sat well in the mix.
BTW, the KSM-32 seems to have the most neutral sound, whereas the 44 has a slight smiley face curve (a little more highs, a little more lows, midrange sounds almost identical). Nothing dramatic, but the 32 is definitely the flatter of the two. Both are extremely well designed and well-built mics that would probably get a lot of use in any recording environment, up to and including a world class facility with lots of high-end prestige mics on hand. I will definitely own one or both of these mics, myself, at some point.
Brad