I don't have a broader definition of pyramid scheme in mind. Maybe people do use the term in a broad sense. Why not just call the broader term "scam"?
from wikipedia:
"A pyramid scheme is a non-sustainable business model that involves promising participants payment, services or ideals, primarily for enrolling other people into the scheme or training them to take part, rather than supplying any real investment or sale of products or services to the public."
Yup. The U.S. Dollar's a pyramid scheme.