Airline clubs have been around for decades and decades. Usually they were promoted to specialized groups like people who flew first class a lot and through travel agencies independent or in house corporate travel agencies. With most companies you have to be "of the level" within the company to deserve such things to be paid for by the company. Or you could buy a membership yourself.
I was a member of the Red Carpet Club in 1972. I think it cost me $75.00 per year. It was nice because you could relax in the lounge with your favorite cocktail and your hostess would come and escort you to your gate "just in time" for boarding. No waiting around the departure lounge at all. You received your boarding pass/seat selection in the Red Carpet Room too. It did take some of the stress off of traveling.
And yes there was a gate keeper at the door to the lounge. At ORD
you couldn't get more than 5 feet into the lounge where a woman at the "front desk" would say "Excuse me sir, this is a private lounge. Do you have your Red Carpet Membership Card?". And it seemed like you had about 10 seconds to produce it.
[Edited 2012-11-22 16:23:58]