Hmmm... Here's my recent experience.
LHR-LAX-AKL (Air NZ)
At LHR full screening of hand baggage. Removal of shoes for screening, metal detector and wand and body search. At LAX, after an overnight stop and re check-in, only hand luggage through X-Ray.
AKL-LAX-LHR
At AKL, even more stringent checks including through the metal detector and HB X-Ray twice and Shoes off for screening. Identity coroboration twice (thrice if you count at check-in). At LAX after another overnight stop, same thing - only hand baggage through the X-Ray.
Obviously secuity is so good in the states that there is no need to do anymore than x-ray hand baggage!