Boxsprings are pretty optional in the US these days, I think, though I suppose most hotels still have them. (I've never had a boxspring on my home bed in my life.)

I've noticed the duvet-only thing when traveling in the US, not just outside. (It's been a while since I've been outside the US, so I don't remember about that so much.) I always have that same reaction: what if I only want a light layer of cover? what happened to modularity?