This same claim gets made about Canada, and I always found it particularly offensive to anyone who isn't an immigrant with a foreign culture. It's a riduclous statement anyway. The south doesn't have their own culture? East vs west coast? Europeans were pointing out yesterday that Americans have different expectations for housing (bigger housing, suburbs), is that not a part of the culture?
Isn't the idea that we are welcoming to foreign cultures, and actively embrace multiculturalism a part of the culture?