One core mechanic lacking in modern blogging: knowing who is reading your work.
With an email newsletter, the writer has reasonable confidence their work is delivered to a known audience. With a blog, the best the writer has are comments and Twitter, both which are totally broken.
There should be better tools for the writer to publish to a specific audience (say, <50 people), for the audience to receive the work through their preferred means (e.g. email at the end of the day vs. RSS), and for both to engage in a productive dialogue that evolves over time.
Oh, and one more important piece: a “Start Here” point of entry for those new to the conversation, so they can painlessly get up to speed.