Or they could have released a non carrier branded model and sold it directly to the consumer, or to smaller cell providers. I live in Alaska, and one of our cell providers was the first company to launch the Galaxy S2 in the united states. How you ask, because they sold the unlocked international version.
Its not "testing" that has to be done on the big carrier phones, its ensuring their spyware works and you can't use a competitors sim card.
http://www.engadget.com/2011/09/09/samsung-galaxy-s-ii-now-shipping-for-100-in-america-on-alask/