Thanks to Russ I discovered a problem in my feeds that caused Bloglines (and probably a few others) to keep on marking every entry as new. The comments counter is automatically incremented each time a new comment is added. Bloglines, in addition of the looking at the entry dates, also scan the actual text. Per Russ suggestion the feeds now include a dynamically generated image to indicate the number of comments associated with an entry. Sorry for the inconvenience.