Let me follow along with your breakdown.
For the guest issue, guest permissions are set to allow seeing the topic list. As a guest, I click on an item in that list, and I would expect to see the message, but I see the CSS styling, and no message. Check out this link:
http://www.wpperform.com/forums/genesis-framework-child-theme-support/
I would imagine you are a guest, so if you click on 1 of the posts, you should see the message. All I see is the CSS styling but no actual text. If I look at it in Firebug, I see an empty <div>.
Your clarification on WP vs SPF admins may have cleared up the other part of this. I was referring to a WP site (not a network) admin. As I mentioned in my original post, if I visit Options->Members, I have administrators set to be part of a group that would be able to read the posts in that forum. I was assuming that referred to WP admins, which was the basis for my question. So I understand why a WP admin is seeing the same thing as the guest. However, that leads to a follow up question:
If Options->Members settings for Administrators refers to SPF admins, there isn’t an Administrator permission set on the Permissions menu. That suggests to me that SPF admins get full permissions (full as in can do anything). If that is the case, what is the purpose of a group setting for an SPF admin?