I think the real difference in allowing/disallowing anon posting is one of atmosphere. When anonymous users are allowed to post, the board has the feel of a public forum. When they are banned, it has a feel closer to that of a club. Granted, the club is hardly exclusive, but still, the overall atmosphere is different.
Over the years I have read Blue's News, I have become more comfortable with the idea of directly associating myself with the site. Now that I am required to, I have registered. However, those that are unfamiliar with the site or don't feel that they are a part of the community will hesitate to take the somewhat symbolic step of attaching themselves, in a semi-permanent way, to Blue's.
When you are not a member, the only association you have with the site is when you log in. On registering, a connection has been established. Even when you are not on the site, there is a server, somewhere, with your nickname and email address. Psychologically, I believe that this is a lot more important than it appears to be on the surface.
This is not an argument for or against anon posting. It is just on observation.