Originally Posted by IAN-UK

It seems unlikely they turn away airline guests: there'll be some sort of contractual obligation to look after them, and they carry with them a payment from the airline.

Lounges routinely turn away PC-type guests when they are busy - but I'm guessing there's a much looser contract between lounge operaors and the providers of this type of perk. Most likely pay less than the airlines, too; so PC guests are admitted on a more or less standby basis.