I think the fundamental nature of a pyramid scheme is that the people below finance the people at the top. In the example you used, the people at the bottom are

I think the fundamental nature of a pyramid scheme is that the people below finance the people at the top. In the example you used, the people at the bottom are not injured by the people who invited them. It would be different if they had to pay a fee to sign up once invited that went directly to the person who invited them. That's the scenario that sets up the people at the base of the pyramid for fraud. In your example, people aren't injured if they can't find people to recruit.