British vs. American cover art

What I don't know about art can fill a book entitled, "I don't know if it's art, but I know what I like." But on a recent trip to England, even I, the artistically challenged, noticed that British and American cover art was decidedly different: American book covers were more colorful, almost garish, while British book covers were more austere and muted. Big empty swathes of negative space filled the British covers, and they looked practically empty next to their busy American counterparts. Why the difference?