Ripple paid a fine of $700,000 for selling XRP to US investors that weren't certified investors. And most people believe that at some point the SEC will try to regulate token sales. If they decide to treat token sales as financial investments in private companies, then immediately, 97% of the US population (that isn't a certified investor) won't be able to buy in. This is just a precaution that most take, but I'm sure that given enough thought to how international law actually plays out, a non-certified US investor could buy into token sales from companies registered outside the US or even US companies since the tokens are similar to commodities, similar to the promises you find in crowdfunding platforms such as kickstarter.