Is it so hard to believe that
Pokerstars, and maybe other sites, have people playing under usernames in their tourneys and cash games, receiving information about hands and which ones to play or drop? That would certainly explain the stories of players with seemingly unbeatable hands being called by players with nothing, only to get beat by the river. That's one way
Pokerstars could make money off of rigging their games, by literally taking it away from their players. There's just too much unknown information to call
Pokerstars legit.