As a Brit who has instructed in the UK for two years I have experienced pilots from training backgrounds in both countries. On the whole the standard of pilots from both is very much the same.
Of course when you transfer students from one country to another it is going to take more than an hour to acclimatise to the differences. I have checked out many UK trained pilots in the US - most of which were fairly average pilots whose RT was not terribly good either.
Covering some other points brought up, dead reckoning is a big part of the PPL syllabus in the states and as I recollect there is a requirement for more cross country flying to gain an FAA PPL than a JAR PPL. Unfortunately it is just something people tend not to be good at whether trained by Americans or Brits.
Full stalls are always taught at PPL in the States, PFL's have huge emphasis, as have stable approaches and crosswind technique.
Maybe you have just been unfortunate with the students you have seen, I have seen the same thing in reverse I can assure you.