No, the people who buy their app are "idiots". Either way 37signals makes money from glorified simplicity, which is both a marketing trick and a good idea.
Do people really spend their time making sites like these for attention? We get it, you're good at using Photoshop and maybe CSS. These sites are useless, why would anyone waste their time making them?
Seems like they are actually following the mantra of releasing a dead simply product quickly, and the slowly adding more features so that in the end, the users might as well have signed up for WordPress or Tumblr or similar sites in the beginning. Clever.
It definitely looks like the mouseover content is manually inputted, but since Microsoft acquired Powerset (http://www.powerset.com) last year, they could also pull some information about topics from it.