The website says it's a Paris thing, which sounds plausible. I wouldn't know about nice restaurants. I'm pretty sure it's expected in regular (for some value thereof) restaurants, at least in Paris: French television movies always show waiters getting mad at customers who don't tip, and my parents (who are stingy with tips) always tip in restaurants. My intuition says that tipping in restaurants is even more important than in cafés, but I don't know why - maybe just because the tip is bigger?

(Remember the second Paris meetup, where I made an ass of myself by complaining I didn't have enough money? I added a few coins to the pile when we left anyway. Not tipping is a mortal sin.)