Outside of Facebook's revenue tinkering, there could be several other reasons to explain Nick's drop in engagement
- Facebook has gotten better at spam fighting. The previous "likes" could have come from bots or other spam techniques. What he's seeing now is actual engagement
- Facebook's user engagement hasn't kept up with volume of graph growth and newsfeed publishing. That's to say, users are "liking" the same # of posts per day, but there are so many more posts in their newsfeed due to having more friends, subscribing to other pages that each friend gets fewer likes per item. Lots of apps/sites publishing into feeds now.
- Secondary effect of ad models. Over the past year more of my feed has become sponsored/promoted. This pushes organic down the page, especially on mobile where app install promoted spots take up so much real estate.
- Impact of mobile. Although the latest FB iOS update created much larger "like" buttons, the previous UX had these as smaller icons. Perhaps as more folks were reading Nick's post on mobile, there were fewer likes per view.
Any other ideas?