I've read the same thing on an exercise physiologist's blog. IIRC he actually did a comparo, with a sleeve on one leg and nothing on the other, and showed how much the un-compressed foot swelled. It makes sense to me, but I don't know anything more about it. Lost the link, sorry ....

I'm in the same place with my feet being wide out of all proportion to the size of my legs. I have one pair of hose that's 30-40 mm Hg that I can only wear for a short time until my feet hurt so badly I have to take them off, but I do wear them as long as I can after an event. Then I have a pair of drugstore brand thigh-highs that I think are 15-20 mm Hg, that I'll sleep in and wear for travel, and I do feel I get some circulation benefits from them without killing my feet.