Russell Beattie recently asked why we don't see more aggregators integrated into weblog systems. That is, why Movable Type doesn't have the ability to read feeds, and why BlogLines doesn't have an integrated weblog system for easy posting. He suggests it is because aggregation is hard (check out Mark Pilgrim's analysis of the different RSS formats and imagine parsing them) but I don't think that is it. First, I think his premise that aggregating and publishing being the yin and yang of the current web publishing paradigm is correct, but the ability to read an item then seamlessly post and comment on it on your own blog, all under one logo, just isn't such a necessity. The two applications are inherently different with all of their own frontend and backend challenges. They are two applications at opposite ends of a process. Just because some of use want to connect the two ends to create a loop doesn't mean the apps need to be developed in the same house. Second, just because someone can create a great aggregator app, it doesn't follow that they would also be able to create a great CMS app, or that they should (or vice-versa). BlogLines is a great aggregator and I love how they just focus on streamlining the reading process. Movable Type is a great publishing tool, and I love how they focus on streamlining the publishing process. It would be great if MT Bookmarklets worked within Bloglines, or Bloglines had an interface to post to MT, but in the meantime they focus on their task and both do it well. I have yet to see software encompassing an aggregator and CMS that is as compelling as MT and Bloglines used individually. Ranchero Software, makers of the popular NetNewsWire aggregator, leverages the various weblog APIs to allow posting from within the aggregator. Also, just last month, they proposed the External Weblog Editor Interface to allow the use of an external editor when posting to a weblog. It seems they understand that the weblog-specific editor is going to be better suited for posting to that weblog then anything they create (or can squeeze through the weblog posting API) and so they open the door into their app, add some hooks, and then go back to making a better aggregator.