It absolutely is. It's a feature that every paying customer will use at least once. I would say if you can't properly support international CC orders/addresses, then make that your policy and don't ask for the country.
There's nothing wrong with saying "Sorry, US addresses only" if you don't have the resources to support international. But if you're asking your users what country they live in, you should have all of the machinery in place to properly process it.
Exactly. If a user is being led to believe that their location is supported, support it. Otherwise make it explicit that it isn't.
You are supporting international orders? Spend a few hours making a comprehensive address verification system and reuse it everywhere. Over time the effort expended on this task will hopefully become negligible. Maybe that'll happen after you get your first international order.
"A comprehensive address verification system" does not take a few hours to make. In another comment on this thread I posted a link to an amazingly detailed address format database and I'm quite sure it took longer than that to make.
I think this would be an awesome open source project!
To clarify: I'm not suggesting that this AVS be made from scratch. That definitely would take, as you say, more than a few hours -- not to mention that it's unnecessary.
Finding the rules and data is but a trivial, slightly time-consuming task. I saw your link before posting my previous comment and took this into consideration: someone reading this immediately has a comprehensive DB of address formats.
"A few hours" may have been a bit ambitious, but over a weekend, and with the required data already available, creating a back-end solution to this is surely not out of the realms of possibility for a reasonably competent programmer?