https://www.sec.gov/divisions/corpfin/internatl/foreign-private-issuers-overview.shtml#IV
IV. Exemptions from Securities Act Registration — Initial Distributions and Resales
"Foreign private issuers may raise capital in the United States through a registered offering of securities or through offerings that are exempt from the registration requirements."
This is a quite complex area of law. What you quote does not mean that all offerings by foreign companies are exempt. Not even close.
"Offerings that are exempt" are typically those which are limited or private in nature. For the Iconomi ICO, any Tom, Dick, or Harry in the USA could buy ICN. So it doesn't meet a limited/private exemption.
Other exemptions require e.g. that there be no marketing efforts that could be reasonably calculated to reach the USA. Probably also a failure. (If they were going for exemption that required this they would have handled all marketing themselves, and not outsourced to uncontrollable bounty program.)
And even if the ICO was properly exempt, resale on the open market in the USA may not be exempt. The SEC explains this with a quote that directly applies to the current situation with not being listed on bittrex or poloniex.
i.e., Iconomi is having a hard time placing its securities on exchanges because it can't establish an exemption for resale transactions on those exchanges. Hence they need to do the SEC registration work.