Kurt, I seem to recall that you rode your camino in September, the start of autumn. Mike plans to begin his camino at the start of Apr - just after the end of winter, when I expect that it will generally be colder. I could debate whether a sleeping bag is necessary at all in September, but having to sleep in one's clothes is hardly ideal. Perhaps doing it for a couple of weeks might just be okay, but anyone walking might have to expect to do that for a month. That's a tough call to make.
The only person I saw doing that was having a pretty awful time of it, and it made me even more glad that I had both a change of clothes and a +5degC bag when I walked in late March / early Apr. At that time there wasn't anyone discarding their sleeping bags, but then I didn't see piles of blown out boots either, so perhaps I wasn't looking in the right places.