If there is such a rule then it is actually kind of prejudiced against people who have a small capital. Personally I've seen ICOs that if you want to join, the minimum you have yo put up is at least 5000 USD. I mean, this really makes investing in such an ICO discouraging. Then again, if you don't want to invest or can't invest then don't.
This is just because of the whales. Whales are like casino owners which never let gambler to win big money. Gamblers always lose their money but never win. The same situation is here in cryptocurrency market. Whales will never let you make some money but always think how to collect money from all over the world. You will not be able to make money and become rich.