It also has to do with risk and risk tolerance. I assume $10 was chosen as an amount that wouldn't hurt too much to lose for most people whereas some people might miss $100. The higher the upside is, the higher the chance you'll lose the money can be and still be worth investing. In this case the argument is that although you'll almost certainly lose all the money you invest into bitcoin, it's still worth it because the upside is so high if bitcoin does end up succeeding.