I was thrilled to discover this hidden line, which, now I know where it is, seems so loud and clear I cannot imagine anyone missing it. I also find it intensely moving, as well as apt - it moves the emotional apex of the film from the very end back to the purgatory of the Twist ranch, turning the subsequent scenes into a wistful epilogue. IMHO this results in a more balanced whole. The story effectively ends with the scene of Ennis driving away from Lightning Flat, which is the mirror image of the opening scene. It doesn't seem right that anything dramatically crucial should occur after that, and now it doesn't, - what the epilogue does bring is a glimmer of hope: Ennis has learned something from his experience.
I do think it is a bit harsh on Ennis to assume that, even in that private, intensely emotional moment, he would not be able to say these words. He IS, definitely, a loving man - only not very talented at expressing it.
Really well put, stevenedel! That's why I don't think it detracts from the movie, either. When Ennis uses the word "love" with Alma Jr., it shows he has absorbed the lesson, and the expressions that cross his face when he looks out the window are very sad and touching. But the scene isn't as powerful as the closet scene, and the idea that he finally says the words to Jack in that moment, right away, without any hesitation -- but still, tragically too late -- is so so so heartbreaking. And if there's ever any doubt that Ennis is a loving man (not that there is), it vanishes then and there.
And the fact that it's so hard to discern -- that 99.99999999 ... (infinity) percent of moviegoers will never even know it's there -- has the effect of making it seem like it's still a private moment for Ennis.
I don't know that I'd downplay the final scene that much, though. I think the new location of the shirts and the "I swear," and even Ennis' decision to attend the wedding are all pretty dramatically crucial.