I think it's true that comments about recent blog posts should be on the blog, but one month might serve that end just as well as three. It's pretty rare that people post on blog posts that are a month old. Not to mention, if there is still a discussion over there after a month, it will probably continue there. Maybe a parallel one could arise here, but I doubt it would take traffic or discussion away from his blog.
The last post on Feser's October 29 post, which received 206 comments, was on November 23.