I can certainly see the logic for that claim if your entire goal for travel is geographic diversity. What about cultural tourism, though? Despite there being a not-unreasonable level of ethnic diversity in the United States, the cultural diversity is decidedly less noticeable; "melting pot", remember. So if I want to travel to experience a different way of living daily life, or to meet people who live in a certain country, or whatever, then it's a little harder to do that in the USA.
As a Canadian, I also lament the fact that we don't have the ability to travel as extensively for so comparatively little as do those living in the EU. Simply getting anywhere else in the world is so frickin' expensive...