I first was irritated by this behaviour too until I closer looked at the forum posts and discovered that there are even more posts that are much wider than the page. I decided to work with this fact and not against that any given width will not fit for every situation. The average of smaller and wider posts makes somehow a medium width. That is no joke. I am working on a way to incorporate those smaller and wider posts in a way that both do not look false. I think those narrow weblog like websites with the postings running into the right bar are distracting.
Struggling against reality is a hard and unsuccessful task
Urs