No it isn't. Imagine that A convinces B to sign up.

A pyramid scheme pays "A" with the signup fees from "B". If people stop signing up, then you can't pay B.

Here, "A" is paid IFF "B" makes money. if B makes no money, then A makes no money. It's revenue sharing from referrals, not a pyramid scheme.

not really; in a pyramid scheme (at least the generally understood scammy sense) you pay money to buy in, and then recovery that money by inducing other suckers to sign up. the money you pay goes to support the people higher up the pyramid.

in this case, the people at the bottom are actually making money, rather than paying it; it's just that some percentage of their fee is shared with their referrer (it comes out of the company's cut, not the user's)