Only thing different with any other pyramid scheme, is the reward system. Usually, pyramid schemes use an individual reward system. Meaning, there is a fixed reward that goes directly to the older member for every new recruit and for other recruits that come after the new recruit. With bitcoin, the reward system is more general. Meaning, if you recruit someone, then everyone who are already in the pyramid will get an equal amount of reward. I think that this is a smart trick, since it makes the community stronger and that will hodl the pyramid together with more strength.