Not 100% sure, but Yahoo can absolutely delete a post if it wants, if a poster asks that his post be deleted, or if another entity complains enough to a Yahoo source. I also believe some public companies will monitor message boards via its own sources or outsourcing to review for misinformation being publicized. Hedge funds
or private companies have been known to present misinformation in order to buy or sell stocks at better prices.
I believe I remember a post this past year that Terry put up stating derogatory items about Lewis, That post didn't stay up too long. probably after Terry realized he could be in deep sh-t for that.