OK, so the reporters of the original Reuters article may have written their story from New York and followed the journalistic standard for datelines. But that in itself is a problem, because not only are New York and Salt Lake City 2,000 miles apart geographically, they are widely different culturally, especially with respect to the subject at hand. I would go so far as to suggest that Reuters' New York writers were chosen to do the initial story because it would be much more gay marriage friendly. So there were no "boots on the ground" for the original Reuters story, which is a major reason why it turned out as biased, inaccurate, and deceptive as it did.
I would be very surprised if Reuters has a correspondent in or anywhere near Salt Lake City. Internationally speaking, Utah isn't that important.
Reuters probably does have someone on the West Coast, however, but that likely would have generated a Los Angeles or some other California dateline.
This New York dateline on a Utah story may end up remaining a mystery that never gets answered because internal story assignment decisions generally don't get discussed because they're usually not interesting to readers.
But who knows? Free Republic being what it is, it wouldn't surprise me if some FOX News or Washington Times reporter shows this thread to a friend at Reuters and says, “Look at the debate you generated!”