First off, let me apologize a bit- I had a raging migraine earlier when I typed my previous response. I didn't mean to be quite so rude. I am usually more diplomatic.
Razorfish- My only experiences have been with:
Amway (before Quixtar spun off): It is entirely possible for anyone in the up/down link to make more money than someone above them. i.e. if you sponsor someone and they really tear the business wide open, and you do so-so, he will "stop" more of the bonus cash flowing up from the dollars being bought. This is fair, and even better, cannot be influenced by your upline (in other words they can't steal volume from you and take credit). This is the case of the guy who makes about half a mil. He himself has a more profitable business than his upline in spite of the fact that his business is included in his upline's "volume"; so he makes more money.
Please note: FWIW my own brother got scammed by a guy in Amway, so I have seen both sides. He got in, then his shitass upline convinced him to buy about 6 kits right away so that he would be prepared when he started sponsoring everyone within 3 feet. He never showed a plan and would not even call his friends, so his upline moved on. Who is to blame? In this case I blame the upline more, because I feel it is incumbent upon him to work with noobs until the point of exhaustion, in order to be a positive role model, and to also not coerce someone to buy unnecessary supplies. But my brother was completely uncooperative, so in the end I feel the sponsor just about broke even, because IN THIS CASE he would have made a nominal amount of residuals off of the 6 or so kits' volume. The Sponsor should have qualified my brother better and determined that he was just not interested.
Melaleuca (sic?): A step-cousin was involved, and he tried to involve my Uncle. You HAVE to buy at least $300 EVERY MONTH in Canada. So in spite of the fact that you may be new and have no sales or downline you still have to buy this minimum. I find this is a normal approach for a conventional biz, like where I work, but for an MLM it sucks.
Tupperware: My wife looked into this. She wanted a way to create income while home on maternity leave. In order to create residual income you had to become some level whereby you had people under you. In order to attain this level, she HAD to attend a business meeting with fellow leaders and her "upline" or whatever they call them once a week. Sounds easy- except that my wife was still working and the meetings were every Friday at 1:00 PM. The most retarded thing I ever heard. Her upline was salivating because my wife led 4 people to her in less than 2 months. She had to give it up because she was making her upline wealthy and she got nothing out of it.
My Dad got into water filters about 20 years ago (NSF?) and some scent-inhibiting powder about 15 years ago. Both required him to invest several thousand dollars to qualify for deep enough discounts to be profitable. He never sold one thing, so all he had was about 50 pounds of expensive sand and 20-years' supply of water filters (which actually worked well).