I completely disagree with that policy. In fact, I don't even believe that it exists.
I know that it appears on a sticky on top of TalkBoard Topics, along with proof of "copious" posts already appearing in ill-suited forums, but the TalkBoard never made a decision authorizing that sticky.
The illogic behind it is obvious: Off-topic posts are removed from forums. Hence, if a post is off-topic it should not be found and therefore can not be used as the evidence demanded.
My policy for a new forum (other than for a flag carrier, which I have discussed elsewhere) would be:
1. It must be travel-related. FlyerTalk can not handle every subject in the world and it is, at heart, a travel bulletin board.
2. The elected members of TalkBoard should vote for/against the proposed forum on the basis of whether they feel it would be helpful to the membership and an asset to FlyerTalk. This is, admittedly, subjective -- but that is why we have human beings making this decision and not computers.
I believe that all forums should be reviewed annually. If one has less than 100 threads in its first year, and 200 in each subsequent year, it should probably be removed. I say "probably" because in some cases, and Disability Travel immediately comes to mind, its value to even a small minority of members is so great that it should continue despite a much lower thread count.