Its quite ironic, USA often blames other countries for being spammy(main target China and Russia) but it itself tops being most spammy in world. I guess this somewhat proves why stereotypes are called stereotypes. Now few non-USA might be thinking then why USA doesn't got banned from websites like other countries the answer is simple most of the websites you are talking about are USA based and by the way USA owns the control of whole Internet. You can see in many USA affiliate networks that "this and that country banned due to excess spam". And there isn't anything surprising because most of the publishers and even customers are from USA so how the hell they can ban their own citizens to access website.] Source: http://www.spamhaus.org/statistics/countries.lasso
The USA is the largest country which uses the Internet so widely - so this info is not shocking to me at all.