"Authenticated User" is not really a role

I've come up against a usability problem that I think is caused by a problem in Drupal's data model.

Example of problem: When setting block visibility settings, it is impossible (without writing custom php), to make a block visible to authenticated users who have no other role, if you don't want that block to show to all authenticated users. In other words, you may want to show the block to all authenticated users except those of belonging to role x. No can do without php.

That's just one simple example. But the problem exists anytime one sees "authenticated user" in a list with other roles because "authenticated user" doesn't mean the same thing as other roles in the list.

One approach toward solving this would be to require the assignment of a role for each user upon registration. Site admins would be required to define a default user role. All authenticated users would be required to have at least one role. Maybe some of the code from the Auto Assign Role module could be used for this.

Meanwhile, "anonymous user" and "authenticated user" would be pulled out of the roles table. Drupal doesn't use the roles table or the user_roles table to determine whether a user is anonymous or authenticated. It relies on the sessions table for that.

It's clearly important that "Anonymous users" should still show up on any lists determining visibility, permissions, etc, but it should be possible to provide that functionality without having "anonymous user" still in the roles table. But even if anonymous user needs to stay in the roles table, seems like "authenticated user" really needs to go.

This topic must have been discussed at length somewhere else, but my searches didn't yield anything.

Curious to hear your responses and/or references to other places where this issue has been discussed.

Shai
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