@samir Interesting point about the recipe sites.
So it's not about showing ads; it's that "user clicked away and then came right back to Google search" is the strongest signal Google has that the result the user viewed didn't give them what they wanted. But you're absolutely right---if someone's browsing through recipes or just needs to duck in to check one thing, that's going to be a strong down-sample signal that it wasn't the recipe the user was looking for.
... not sure how they can control for that without killing the larger signal, which is actually very useful (and tends to also penalize, for example, sites that don't load because instead of showing the information they're slogging through ad loads... Users click away from those too).