yeah, that easily makes sense...
If each command is a half second faster, then 120 actions would save 1 minute. Lets say it's slightly less for simplicity and go 100 actions per minute. One craft at spam craft (again for simplicity just hitting enter button rather than for exp bonus) might require 10 inputs per 300exp, at least in my experience... 300x300 = 90,000exp, .. and 300 synths with 10 inputs is 3,000 inputs at 1 minute per 100 = 30 minutes faster for the Japanese per level of high level crafting. even in the 30's this would still equate to 20 minutes. 30 minutes x 10 levels = 5 hours + 20 minutes x 10 levels = 3 hoursish = 8 hours per craft levels 30 to 50.

Across all crafts to 50 this would then mean we are spending an extra 60 hours give or take in lag over the japanese.
That does not include gathering and battle classes.

0.4 seconds may not seem like much, but it adds up.

Another poster on these boards made a very good observation last week, saying that if there is no local server set up for players outside japan, this game will never really succeed no matter how good 2.0 is outside of japan. Those tenths of a second crush a game.