You can calculate the GDP per man-hour to compare "smartness". Of course that doesn't mean individual workers are doing something smarter, but that together they've built a system which operates more efficiently. Maybe past generations of Germans spent their work doing something that benefits current generations (figuring out how to make reliable car parts?), while past generations of Greeks worked on less helpful things (tourism?).

Actually this was a joke. And yes: If you want to achieve something other than just getting a mediocre paycheck, you should put in the usual extra hours.

But afaik there also seems to be a slightly different work mentality here in germany, where you go to work and actually work, not chatting gossip or read facebook... at least some blog post from non-germans claim this (since I'm obviously biased I can't confirm this).