It seems there is a law (supported by the French booksellers' union) in France which makes it illegal to sell books at a discount of more than 5% off list price. Last December, the booksellers' union took Amazon to court, and it was ruled that Amazon's free shipping is illegal in France because it constitutes a discount of more than 5%.
Faced with a fine of €1,000 per day until they comply, Amazon has decided to pay the fine and keep offering free shipping, while gathering signatures on a petition to have the law changed. (So far they have over 120,000 signatures.)
Perhaps the theory is that if everyone has to sell books at list, then French shoppers will pick their bookshops by picturesque location and charming staff. Still, I find all my sympathies with Amazon on this one -- and the poor French public, who are stuck paying list price for all their books.