I thing you should review your informations,according to OCDE 2007 report, foreign born population as a percentage of total population are 12,2%  in Sweden and 12,8% in USA. At the same time, in countries like Spain, latin american people are 37% of inmigrant population while in USA they are only the 25% (= % for Netherlands), so even more, many people prefer to cross the ocean before going to the USA.