While a true Pyramid scheme or Ponsi operation is indeed illegal, MLM is not. The difference is that to qualify as MLM, there must be an actual product or service which is sold to people who are outside of the program. It still isn't exactly the way to fame and fortune, since it does count on being able to recruit enough underlings to support it and make a profit, which very few MLMers ever do. In practice, most sales of AMWAY products end up being purchases by the distributors themselves for personal use, hoping to keep their sales volums up until they are promoted to another level. The products are expensive, and non-competitive when compared to what you could buy the same stuff for at any department store.
For some reason, many JW's are attracted to such programs. Perhaps it is from the connections they have with others in the organization, or perhaps because it is something that can be done at odd-hours. Can't say why, but more than once someone at the old Hall would stumble into it and be on a recruiting drive for a few weeks, until they burned out.
It is interesting to note that Amway has an implied "Christian" theme running through it, and the bulk of its distributors proclaim their Christianity quite openly in sales meetings.