There was an interesting article in the Economist last week (
http://www.economist.com/world/europe/displayStory.cfm?story_id=1560497) subtitled "Why France continues to annoy the United States". It's point was exactly what you concluded, that they will come on board in the end.
But the reason they are holding out is not conviction or even diplomatic blackmail. If they go along from the beginning, they are just another ally. By holding out, they are like the spoiled child in class who keeps acting up to get attention.
The money quote, from a State Dept official: "What matters to France is that they matter."
FP