I've yet to meet any of these people. Everyone I saw crossing the finish line in 1 day at STP was wearing cycling gear. Most of the randonneurs I've ridden with or talked to all swear by their favourite brand of padded shorts or bibs for anything over 200km. It's rare I see anyone riding a century in something other than bike shorts/bibs.

Now, I will agree about the Merino wool, though. As an avid hiker and camper, I own quite a few Merino wool garments. They're warm in all weather and they don't tend to get as stanky as synthetics if you wear 'em for a few days in a row without washing.