Will you people talking about CD rack construction please change the subject and start a new thread? This has nothing to do with Frank choosing speakers.
Ah! But Frank has already chosen his speakers. And what fun is it to actually stay on topic?
His command to stay on topic was, itself, off topic.

Rigidly moderated fora (including Usenet and mailing lists) stick to the topic very well, but can also be boring and even not very informative.
Threads evolve and devolve everywhere else, and there's always somebody complaining that people should stay on topic, or start a new thread, or change the subject header, etc.
Dan, I understand that this bothers you, but it's not likely to change. I've been on the net since '94, and was on the BBSs before that. I've seen literally thousands of threads and discussions, and threads evolving and changing is simply part of the nature of the beast. I think you're wasting your time by constantly complaining.
You can figure out how to handle this in some way that's workable for you. Or you can select only rigidly moderated fora that don't have this problem. The third choice is to avoid the net completely.
I actually did fork a new thread at one point in this thread. My fork died after one response or so. I've observed similar things in the past and it usually seems that you get more discussion if the original thread wanders than if you fork a new one.