1) It's well-known that U.S. providers achieve closer to advertised speeds than European providers. That's why the U.S. does way better in Akamai's tests of actual bandwidth than the OECD's study involving advertised bandwidth. The U.S. is currently 8th for highest average internet speed in Akamai's most recent state of the internet: http://www.akamai.com/dl/akamai/akamai-soti-q313.pdf?WT.mc_i... (see page 13).
2) It's not adjusted for price level in each country. Many things are cheaper in Hungary or Slovenia than the U.S. Internet service isn't a commodity good like an iPhone where everything is assembled in China. Internet infrastructure is put down and maintained by (often unionized) U.S. workers earning U.S. wages, and sold to customers also earning U.S. wages.
3) It ignores the cost of government subsidies: http://bits.blogs.nytimes.com/2009/03/12/the-broadband-gap-w... ("There are only a handful of major projects worldwide to build fiber lines to homes that don’t involve significant government aid of some sort, Mr. Burstein said, including Verizon’s FiOS and Iliad’s fiber network in some large French cities.").