Difference in length of study between Europe and the states?
Your understanding of the duration of PhD programs in the US is a bit off- the average "registered time to degree" beyond the bachelors degree for PhD recipients in the US is more like 7 years.  See

[http://www.nsf.gov/statistics/infbrief/nsf06312/][1]


In recent years there have been some attempts to reduce time to degree, and the data reported in this link are more than 10 years old, but the situation hasn't changed very much in the last 10 years.