I've only got 3 horses, but they don't spend even 1% of their time actually touching each other. Standing within 12 inches of each other? They'll do that for hours, and often within 6 inches. They couldn't stand that close to each other for as many hours as they do without actually touching each other unless the physical contact was in some way inappropriate to their sensibilities.
The only physical contacts my mare seems to really accept are 1) head rubs at the end of the ride, which I think is a learned behavior telling her work is done and feeding is about to start, and 2) having her mane fussed with. She will stand as long as I want if I'm untangling her mane. If I rub her shoulder, withers or hip, she accepts it for about 5 seconds and then moves away. The only exception is for an occasional itch that she cannot reach.