The FAA and CAA/JAA are 2 completely different organizations. The question could be why does Europe have variable and low TA's? On QNH you have an accurate terrain clearance, while on flight level, "pressure low look out below" isn't an issue when in the USA but could be if flying in Europe because you'll still be FL70 when MSA is 5500ft with a QNH of 970mb, or when climbing to level off at FL50 when QNH is 973mb. By the time you set standard (1013), you may bust that level! I think there is some merit with higher Transition Levels. It seems consistentr and safe.