I'm not sure about this, but it is possible that The New Yorker had less space available for AP's story. They probably depend a lot on ads. Sometimes the number of pages of an edition depends on the amounts of ads they sell before the edition is put together and sold. I know some newspapers work this way. I'm not so sure about the magazines though, but I suspect it might be the same situation.
Well, space is always an issue but if this was such an integral element to the story, I think she would have argued for it, space be damned. I guess we'll never know. One thing that is interesting is that I really feel it makes it as if there are two Brokeback Mountain short stories. There are other differences between the two versions, but the absence of the prologue paragraph has the biggest impact on the narrative.
Speaking of newspapers, did you read the bus plunge story, Natali? For others who might be curious:
http://www.slate.com/id/2152895/It is funny, I thought.
Leslie