I checked the milk in my apartment's fridge. My room mate's only lists a pull date and has no other handling instructions (not even to refrigerate). The milk I am buying /now/ happens to mention, in otherwise completely ignoble and normal looking text in an out of the way area, to refrigerate and use within 7 days of opening, but not past the printed date.
I would hazard that most consumers have read the directions on milk /maybe/ once, if at all, and have been operating on prior behavior since then.
Section 4, paragraph 3, point 2 says that milk subject to 'aseptic processing' (defined earlier in the same doc, as milk that can be stored without refrigeration in a hermetically sealed container) must be labeled with the words 'keep refrigerated after opening'.
UHT isn't some magic process that allows milk to sit in an open container for months.