I'm in the US and as an entrepreneur I set my own hours - that said, under these guidelines I would have a severe problem working in Europe.
For one - and this is not such an easy question - "what is work"?
Seriously - as a consultant am I working when I read and search/monitor the web? When I'm thinking about a client's problems in the shower? What about when I attend a networking event in the evening? (Martha Stewart recently had this problem due to her attending an event - she claimed and I would tend to agree - that her attending such events was part of her job)
And for another, a lot of my work and those of many other consultants and IT professionals is cyclical. I spend relatively resonable hours in research and preparation, in the meeting with clients and preparing, but then frequently may have extremely long hours as we reach significent milestones and deadlines. (One project involved a call Friday morning, working all day and night to understand an app which had failed, then all day meetings on Saturday and Sunday to create a solution which could be rolled out early morning on Monday).
Which points to just one of the other issues involved - extra time is frequently needed in the middle of crisis - and it is unlikely that people will be looking at their watches and in the middle of critical events leaving saying "well that's my 48 hours for this week - see you next week" (if anyone I ever worked with did this, I doubt I would ever work with them again. Yes there is a time and often a need to take a break and recover, but there is also at times a need to stay and finish.