Also, if it wasn't for Ang (among other things of course--and of course, he left some of my favorite things out as well)--Ennis might just as well have snuck those shirts out under his jaciket. Jack's mother has nothing to do with them in the short story...except, of course, that they hung in her son's closet for 20 years, and she may well have been aware of them.
Altogether, the movie has more romance, and less sex than the short astory...