I would argue that at least DFW (and possibly the author) knew exactly what he meant when he said irony. I think maybe irony is misunderstood as necessarily being obvious and bald-facedly deceptive in a noticeable way. I think a lot of the problem DFW was addressing (and I very much agree with h here) that it's so pervasive that we don't even perceive it's ubiquity culturally, and that our modes of communication are so shot through with the stuff that we can't just break down and communicate directly. I could be wrong, but in that sense I thought he was frighteningly prescient. I may be (probably am) mis-reading you, but arguing that irony is important because irony was important doesn't quite work as a counterpoint for me in this case.