If I understand Ellen Lupton's article correctly, it makes perfect sense. As designers we are to design for the user of what we are creating not just some joe-blow who descided to pick up that particular item and read it. Or the writer who just fills in all the information.
You might be thinking, "well duh!" I knew what I was designing and who I wanted to target. But was I actually designing for them? Was I going to reach the audience I wanted to or was another going to like it?
First and for most the user is the number one person. And in return we as designers get feedback and information on our users/audience, whether its in the younger crowd (teens to mid thirties) or the older crowd (60+) and anywhere in between.