For what it's worth...
I was one of the more vocal participants in the thread being discussed. I said my piece, replied when asked a question, and freely participated to the level I felt inclined to do so. Once the discussion began to get redundant in my personal opinion, I abandoned it. I did continue to read it, and became bored with it quickly.
IMO that is what prof was talking about when he asked if it was still serving a useful purpose. I could be wrong about that; you'd have to ask him.
A moderator stepped in AT THAT POINT and after (I assume) reviewing the thread and evaluating it for its continued validity versus its potential for flaming, deemed it no longer valid and closed it. That's why there are mods (well, one reason anyway) on boards like this.
Should one or more participants in the discussion decide to cointinue the discussion, I am certain someone will create a new thread in which to do so, and that the same standards would be applied to it.
Having been a mod at another site, I will say that I admire the standards here. Never once have I seen one closed prematurely; if anything, some are left open too long or not caught in time before things get nasty. The level that is maintained here is the primary reason I chose to hang a hat in these parts for awhile. People are allowed to discuss, disagree, and disagree vehemently. Still, sometimes a topic has more than outlived its usefullness. When that happens, it needs to be locked.
No one forces any of us to be here. If at any time I feel like things are not being tended to in such a way that it makes me unhappy, I'll vamoose. I've done it before, and I'll likely do it again.
Now, let's all play nice, have a Coke and a smile, and get on with our lives.