James,
I agree.
I don't see the moderators role as one that provides structure to discussions. This is a free environment and if people go off on a tangent that is up to them and others involved to pull it back to topic. Many times the tangent has been more interesting that the initial thread.

In saying this I'm not trying to encourage people to hijack threads just keep the discussions interesting, This is by far the best forum on the net. Lets keep it that way.