Ang seems always to tend to make things spare.
I have to recall my very first viewing (before reading the story). The lake scene argument was so intense, so much anger and disappointment, ending with Ennis's collapsing.
Then, such contrast with the dozy embrace, seeing them young and in love, and so tender (in a way we hadn't seen since TS2) was overwhelming to me. What particularly struck me, besides Ennis's humming, was the look of utter love on Jack's face as he watches Ennis on horseback depart.
That face is then replaced by older Jack's resigned, hardened face watching Ennis's truck depart. I think then one realizes the DE is Jack's memory; that makes it all the sadder.
I personally think it more effective without an earlier DE.
Of course, later, reading the story, I found it the most beautiful passage. The story DE is certainly sadder than the film, because of Ennis's denial.
Here's what Annie wrote about the DE:
The most difficult scene was the paragraph where, on the mountain, Ennis holds Jack and rocks back and forth, humming, the moment mixed with childhood loss and his refusal to admit he was holding a man. This paragraph took forever to get right, and I played Charlie Haden's and Pat Metheny's Spiritual, from their album Beyond the Missouri Sky (short stories) uncountable times, trying to get the words. I was trying to write the inchoate feelings of Jack and Ennis, the sad impossibility of their liaison, which for me was expressed in that music. To this day, I cannot hear that track without Jack and Ennis appearing before me.(BTW, here's the gorgeous youtube flashback in slow motion with the music she mentions:
http://www.youtube.com/watch?v=yi6i8bfwV-w)