just wanted to comment a bit with this one,as an avid fan of labs i find your statement to be very unfair with regards to your description of american labs.
1st is the fact that english labs having had a heavier stature is more prone to orthopedic problems such as hip & elbow dysplasia.and not all american labs are lighter build,perhaps there is a confusion with FIELD TYPE LABS (have lighter bone,slender builds,long elongated skulls with narrow stops,longer legs & a very active temperament) and SHOW LABS(heavier blockier builds,low key temperaments,blocky heads with emphasized stops and shorter legs),not americans & english,since most american types are founded based on english bloodlines (such as the late veyatie driving along is from UK & NZ based stocks).
2nd,is the fact that OFA or orthopedic foundation for animals along with the PENNHIP or pennsylvania hip improvement program is located & developed in the united states thus more american dogs are screened with those registries than european imports/stocks.
furthermore,what ever the type a lab has,it still have the even and outgoing temperament that is a hallmark for the breed...goodluck with your beautiful labs