You're missing the point. I'm well aware Sprint phones are locked, but at what point are they locked? I can't imagine Apple keeping a stash of locked phones sitting around, but the more likely time would be once it's registered on Sprint's system, the lock would come down to the phone. It wouldn't make a whole lot of sense for them to sell the phone both here in the states and overseas, but not make them interchangeable.
I could be wrong, but it wouldn't make sense from a cost stand point to have a bunch of Sprint phones that couldn't be used as overseas models if they weren't selling here, since they are already US locked phones.