The rule is mainly for a handful of direct online competitors that are frequently linked to, often ones that are more expensive than FastLane or AllPartsExpress. A lot of people find the forums via Google or another search engine, and aren't even aware that they can buy parts directly off this site! It's really meant to encourage members to help other members by linking directly to the FastLane or AllPartsExpress listing for the part(s) needed vs direct competition.
I am not discouraging open speech or thought on this subject, so I am leaving this thread open!