It's still there - it's just the recent activity notification that says 'x liked x's post', he's removed that.
I like liking well-put posts, but sometimes they can distract from an argument - the person on the less 'liked' side of the debate can be focused on the likes rather than the content and feel ganged up on, though it's an irrational response.
It has been used as a criticism before, 'sitting around liking each others posts and not being interested in real debate.' I don't think it's a valid one though.
I just think it's a useful way to say either 'thanks that explained things well for me', or 'I enjoyed the way you put that', without having to spam the thread with unnecessary posts.
Anyway I don't use recent activity, I just do 'new posts'.