Why do I care about the extra stack height?

Because it made the difference between using the modified through-headset brake stop I was using as the upper part of my decalleur mount (to help firm it up) and not having room for it afterward. Not only could I not use it, but I didn't even have room for a super-thin washer at the top and had to use locktight instead on the headset locknut.

I ended up having to install an ugly Minoura accessory clamp directly on the 22.2mm stem just above the headset and needing to make a new longer custom aluminum stay from the higher position to my bag decalleur. It's nowhere near as pretty or slick as my previous solution.

So yeah, stack height matters. And many vintage steer tubes just will not work with the frames they came with and the Grand Poohbah headset. It's a usability thing. If it weren't so darn tall it could be used as a replacement on a larger variety of bikes. It is always easier to add a washer or two than make the steer tube longer after the fact.

For me it was either put on the ugly clamp or throw away the vintage Reynolds 531 fork and replace it with something that has a longer steer tube -or use a different, more costly and less sealed-bearing headset. I knew it was close -but a mm or two too tight.

I thought about having the ridiculously-large melon-headed threaded top race milled down a little bit on the top a couple of mm but because of the way the wrench flats were situated it would have required more milling to bring them down as well or have no flats at all. It could have been done -but changing the mount and disposing of the headset stay was simpler.

My point being that if VO would have only made the stack height a couple of mm's less it would be a much more handy headset that would cover a greater variety of bikes -or make a shorter version too as well as the melonhead version.