So, America's Going Steady With 'Survivor'

I saw this article from the Washington Post late last week and forgot to post it, but I found it to be pretty interesting. It takes a look at the 18-49 demographic, and shows which shows have "emotionally attached" viewers. Ringing in at number one was Survivor, while some other popular shows didn't have the attachment that I expected. In fact, many of the shows that I deem successful were not considered to have emotional attachments according to this study. Wonder why?