Continental USA (ie 48 states) has 4 time zones. Customers increasingly want more point to point flights. This has led to the use of smaller planes. So, demand for A380s from this market will be limited to a handful for the most popular routes and times.
The global picture is quite different:
1. As posters have noted, Asia is a large market that requires large planes.
2. Lots of long-distance routes have small daily 'windows' when flights are commercially possible. This situation is due to the interaction of timezones, flight times, night airport closures, airport slot availability and airport altitude issues. Perhaps it's not the best example but think of LHR-JNB. BA does 2 747s about 4 hours apart, then 20 hours till the next flight.
3. And there is a growing market for very cost-sensitive long-distance flight. Why else is Emirates buying A380s?
If US airlines and manufacturers think that the global market will inevitably converge to look like the USA domestic market, they are going to have to rethink.
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