This, I think, is symptomatic of what is wrong with the man in general. As I've said before, what people think and feel is not something he can care about nor is it something that he wishes to concern himself with. Most of the strip's conflict comes from his inability to even stop to consider that merely because he thinks that marriage is supposed to turn a woman into a happy homemaker and childbirth into a loving mother that that is not automatically the case. The same man who doesn't see the unfair, unfeeling and unkind moron who threw his child under the bus to play with trains we do spent his life being baffled by people who don't do what he expects of them.
That being said, Elly's reaction to this admission is even more annoying. She is startled by it but the revelation that who she is is a distant second to her looks is soon forgotten. This is to be expected because Elly only thinks that she knows who John is and tends to forget anything that reminds her that he is not especially nice nor does he especially care about what people think as long as they do what he expects them to. It's sort of depressing to watch the poor woman think that if she isn't careful, her husband will become a stranger when she doesn't know who he is in the first place.