This is what my office looks like from 12:30 until around 1:30.
After a year, I guess I had stopped noticing. But our new AE from Toronto recently told me, "I can't get over this mass exodus during lunch!" She used to work in New York, where it was common to have lunch delivered to your office so you didn't have to leave work. And unless it was a particularly slow and sunny day, my lunch breaks in Chicago rarely went past 20 minutes.
I don't think it's a matter of Americans working harder than Europeans. I think it's Europeans doing a better job of drawing a line on how much office life can interfere with inalienable pleasures.