I have not read the book, but from reading some summaries and commentaries, I got the impression that other people took the message as being different from "marriage makes your life measurably less happy" as the chart implied.

The figure takes on a different meaning, however, when we remember that “How satisfied are you with your life?” is not a simple question. When answering it, people think of significant events in the recent past or near future. People who are recently married or expecting to marry are likely to retrieve that fact, which affects their answer. But those who are not do not think of marriage when answering. The graph could be read as the likelihood that people will think of their marriage when asked about their lives. This demonstrates once again how we are “blind to our blindness”—how we are unaware of the heuristic mistakes that we make. In evaluating this graph, people do not understand that respondents have substituted their answer to how satisfied they are with their life with how easily they can think of happy events in their lives.