As a UK exhibit design house, we feel it is more cost effective to both build in UK and ship and to use UK labour to install, than going the US route. UK labour is more multi talented than their US counterparts.
I have just returned from a project in Las Vegas. We shipped an existing stand over and albeit that it was not a complicated one it was cheaper to do this than have the components constructed within the UK. However I did have it built by a US contractor (Nuvista), as there was no way the union laws allowed me to construct the stand with my own staff. I found that their customer service was excellent, and their skills more than up to the job...indeed many of the stands, double deckers, great finishes, were all constructed in the US. Where they fall down is if you find yourself lumbered with unionised venue carpenters, electricians or carpet layers, rather than using a genuine 'exhibition' contracting crew. I found the electricians and carpet layers to be pretty terrible. No-one in the hall even on a show of the scale I was at even attempted to spec a carpet cut in! Most contractors though, and certainly Nuvista, also do Carpet, AV and all of the other services as well though. So I wouldn't generalise about the labour talent. Like anywhere else you just have to look around, and choose carefully who you work with. Here in the UK if you went with general agency labour, heaven knows what you might get unless you struck lucky!
Several exhibitions in the US proved to us that a UK crew is hard to beat and would build and ship UK stand to US anytime. Unfortunately we still have to use US contractors due to their union laws and most of them are not skilled which makes the get-in and a lot more stressful.