If I post a message which is obviously not an advertisement and makes reference to a topic or image in the grid (or even saying the word: Grid) then by my understanding it is on-topic.
I relinquish your right to determine the content on your site and I understand your need to "keep the topic on target" but I believe that your methods so far are disturbing.
First: A nice contact explaining what it is that you feel is "off-topic" about the post would be a welcome change from your tactics so far - Which is to just remove/move those posts that you judge to be undeserving. I also noticed that some of your personal posts to the off-topic group have been removed.
Second:A FAQ or some guidance as to what you base your decisions on would be nice. I DON'T want to post off-topic messages and I won't - If I have a better idea of what you have in mind.
As you must know- I am a long-time supporter of you, Ed, SITO and online collaborations in general. I am so grateful to you for reaching out and providing a wonderful resource for artists and lovers of art.
So, please don't take this personal. I just feel the need to remark upon what I recently find to be a distrurbing trend.