Starring: Ralph the Wonder Llama
Seriously, though, I think nobody here minds being a pedant and saying, "So, back to what the OP was asking..." if they have something on-topic to add. Otherwise I think the OP can assume everyone who had something germane to their personal situation to say has contributed.
If the threadjack convo takes off while there is still a healthy on-topic discussion, that can get confusing, and I think it's reasonable to ask people to start their own thread. But, it takes two to threadjack (or something) and the original person making an offhand comment probably didn't know it was going to get so much response.
And people seem pretty good about not threadjacking journals.