So in the US you don't have to give explanations? Damn that sucks for the ex-employee. In France you have to write a report in order to fire someone unless they're in their trial period.
The right solution, in my opinion, is allow fire-at-will like we do in California, and have thorough unemployment benefits so that it's not worth making a fuss over.
The Zappos model [2] of $2,000 bonus for quitting one week in is great, I wish more places would use it.
[1] http://hrmagazine.be/fr/newsitem/la-france-au-top-des-cotisa...
[2] http://www.businessweek.com/stories/2008-09-16/why-zappos-of...
Some other states are more employer friendly, and others are less.