What's the deal with having an underdeveloped sense of irony?

From the New York Times profile of Jerry Seinfeld (emphasis mine):

One Friday in early October, Seinfeld took a private plane from New York to Kansas City, Mo., told jokes onstage for 75 minutes, then flew to Milwaukee, where he was booked at the Riverside Theater the next night. On Saturday morning he wanted to see “Argo,” so he rented an entire theater at the local movie palace, the Oriental, and watched it with his opening act, Mark Schiff, and his tour producer. “I liked it,” Seinfeld said later on, over coffee at his hotel, “but the ending was a little Hollywood.”