I was just down in south Texas yesterday riding a century, which I rode in shorts and T-shirt. Nice. Got up this morning, and it was 39 degrees, had rained, with a hard wind blowing. That would have been the pits to ride in. Glad I didn't have to ride today.

Something else I thought about is that on a typical century ride, you go more or less in a circle, and if the wind blows the same way, you've got a head wind half way, a tail wind the other half. With a cross-country route, you could be riding into the wind a week at a time. That would get old.