That's like asking for news references for somebody being kicked out of a bar (doesn't matter whether it's unjust).

It just was a common thing - posting links to competitor sites gets you disciplined and possibly banned. Of course, competition was not for money, but for people. Cause if nobody comes to your site, then your ego is hurt and you're depressed. Also posts advertising other people's sites spoil the mood in general, contributing nothing.

EDIT: There were also friendly\allied sites, of course. With little banners somewhere at the bottom of the page leading to those.