I can't say why they don't run afoul of the laws, but my realization of value of a system was due to Bitcoin. For Bitcoin to have 'monetary (dollar) value' people have to exchange 'real money' for them, putting monetary value into the system. This money becomes the pool of money or value that the system has; Ponzi schemes require that new users are providing the cash to pay the old users, but a ponzi seems for early users to be about constant guaranteed return. There is no guarantee that a whale won't take their holding out of BTC, but that's their choice, not a requirement of BTC, even though the new users (investors) are providing that cash.