Grunf,
I have worked as a contractor in the US and am able to comment on skills of "assembly personnel". I was not directing the superior skills comment at design engineering personnel.
Basically a traditional UK assembly worker/fitter/mechanic will have an apprenticeship of 4 to 5 years. The first year is spent in a training school, no where near an aircraft, before being released on the shop floor with at least 12 different experienced fitters in 12 different sections over the three to four year period. Most of the US fitters are what we refer to as "semi skilled" having training measured in months rather than years. For evidence go and have a close look at 2 new 737 leading edges. You will see they are not the same with steps and gaps clearly visable to the naked eye. Then check out an airbus leading edge..all are identical with steps and gap tolerances checked with fine feeler gauges.