Heh, I'm pretty sure bike shorts were a big thing when I was in kindergarten, circa 1990, so I'm not surprised we're seeing a resurgence!
I mean, pretty much everything about human life has been getting progressively more comfortable: houses, transportation, medical and dental care. So of course clothes will move in that direction too.
It does make sense to me that formal wear tends to be a vestige of older social norms, whereas leisurewear is where acceptability progresses most quickly. Formal wear is for situations where you're rubbing shoulders with the enforcers of the social order (religious leaders at wedding ceremonies, bosses at job interviews, judges at court appearances, etc, which tend not to be the time to bend the rules or push the envelope.
Ginger -- I was a bit surprised to see him lump girdles in with footbinding; corsets perhaps. But then, it was written by a guy, and if the editor was a guy too... I think a lot of men view a great deal of women's apparel as basically torture devices. I had a feeling that this pattern could be traced back even further; thank you for providing examples!
Ummlila -- I like to "save" my gear for when I'm actually doing physical activity too. I do have a few crossover "gear-casual" pieces, but they are becoming fewer and farther between. It's fun, though, to think about things like wool sweaters as the gear of yesteryear!
Lisa p --Yes, "workwear" like jeans and boots are a parallel phenomenon! I think he talks about that in the article. Actually, part of the reason I end up in jeans so often is because I use them for dirty chores and they really are the best in that regard. Explains why I have no designer denim, for that matter. Still a hard concept for me to wrap my head around.
Sorry, I'm on my phone and it's tricky to reply to everybody. I'll be back with more thoughts later.