Why aren't State options non-default countries (outside UK) showing for billing address on the contribution page of a webform?
I had this problem too on the main Civi911.com checkout form, and then I was all the more sheepish when it turns out the issue was reported by my coworker Tyrell for one of our clients!  It's a bug in 7.x-4.11 and earlier: https://www.drupal.org/node/2516936

If you upgrade, the state/province in the billing address should update along with the country.