I think this is a case of "all things in moderation". I've seen plenty of threads where the initial point was lost along the way, often times by no doing if the OP. Sometimes that can be frustrating, especially when you're the person asking the question in my opinion.
On the on the other hand, in the thread mentioned (how heavy to build a mill stand), two posts were made, each ending with an off topic comment before the posters (OP included) were chastised. For me, there was nothing wrong with where the thread was going, it was three sentences of fluff.
I think it is also perspective dependant, I find that I rarely go a day reading posts on here without someone, usually one of the many seasoned members who make this place really worthwhile, waxing on about how the younger generation doesn't get it, the condemnation of all things Asian, or making comments about the perceived superiority of the classical tradesman over engineers or other "elitists". To me these things are all horses which have been beaten into glue and don't add anything, but I skim over them because there's probably a nugget of gold in there somewhere.
I view forums like these as a place to commune with friends; I often call a buddy up to ask him something and we usually chat about kids, crazy ex's, or whatever else while we're on the phone. I don't need the conversation to be sterile for it to be worth my time to read. That's just my take, if it isn't what the management wants, it's their forum.