Not surprising, just fascinating how good they are at it. Each headline begs a simple "who, what, how, why" question. Often I click on things I don't even care about because I...just...have...to...scratch...that...itch!!! :)
Not sure how many people become immune to such enticing headlines after a while and how these may undermine a domain branding, e.g., people may stop clicking on search results pointing to that domain.
Even if you develop a tolerance, it might be the case that the regular news doesn't seem as interesting or enticing anymore. While other news sources might actually summarize in a headline, and so deprive you of that need-satisfaction dopamine loop, HuffPo creates the itch (WHO was it?) and then scratches it once you click (AHH, Rick Perry).
HuffPo knows that the population smart enough to do this is a minority.
It is interesting that HuffPo bucks the trend of Google-friendly keyword-stuffed headlines, and instead drives for linkbait title to win social media link juice.