My answer, they don't! Search engines don't give special treatment to sites who publish content only on popular or engaging subjects, period! Its up to those who use the internet to decide what they search for, Google or Microsoft could care less. Here's an example: I write SEO, web design, computer networking tutorials, blah, anyways, I also have games on my website, and while I rank well for a lot of my tutorials and articles, my Pacman game page is now my #1 page on the entire site, getting thousands of hits a week! Pacman is nothing new, and by the way the game is a remake of the original pacman game, nothing revamped or anything like that. So all that up to date content I create doesnt necessarily even matter since its the pacman page that brings home the bacon scoring for over 40 sets of keywords! Hubpages apparently has it all wrong!
What search engines do care about is the quality of your content, NOT what the topic of your content is.