Many social phenomenon are most easily described in this way. Generally, the easiest way to find out who is is a member of a subcommunity is to ask other members of that subcommunities.

And as Migeru said, its a combination of that influence among the rest of the mainstream media - and thus general public discourse, which they catalyse - and audience numbers - some influential magazines are more "insider media", being read by those that make the news, but not really bringing these news to the public.

Auferre, trucidare, rapere, falsis nominibus imperium; atque, ubi solitudinem faciunt, pacem appellant.