Pure speculation here, but my guess is that this has to do with different models being certified by different bodies. IE, perhaps the model sold in Europe is subtly different and hasn't passed FCC or some other certification for use in the states, ergo, they lock them to where they HAVE been certified. Doesn't change the fact that I wouldn't buy it, but I don't think it is something that is done for some evil reason…
If it was a certification issue it would affect every mobile device by every device manufacturer. My guess is that this may be an attempt by Samsung to crack down on grey market imports of their devices. The author suggests it might be a requirement buy carriers, but again that would affect more than just one manufacturer. At the moment we're all just speculating.
Why would they want to do this? I could understand it in the case of a low-priced device intended for poor regions of the world, but this is a high-end phone that is presumably a similar (high) price everywhere it's sold.