For my guess on France: infightings, backlash, EU economy and the trend on maintaining conservative legislators and leftist local administrations, despite national leanings.
I know. These are weak reasons. I'm relying more on my instincts. Not on my wishes, thought.
Legislative elections will be held right after the presidential elections in the summer of 2012, and after that would be held after the 2017 presidential elections in the summer of 2017. If the left wins in 2012, it is extremely likely they would win a governing majority unless for some weird reason the voters behave unusually bizarrely and elect, for some reason, a right-wing legislative majority. And assuming the left wins the 2012 legislative elections, there is no reason to assume they wouldn't make the legislature last a full 5 years until after the 2016 prez elections. The synchronization, if it lasts (I see no reason to assume it won't) basically blocks any cohabitation.