At the UW I had a French Professor who presented a theory about this subtle but distinct cultural difference. He says it all comes back to religion. The French are a historically Catholic society while America is traditionally Protestant. When you enter a French Catholic church you see a large cross with a dead or dying Jesus on it. Jesus usually doesn't look that good (understandably so) his head it hanging, his body is limp and blood is dripping from his head, hands and from the slash on his side. When Catholics look to the cross they see a mangled body. Now, when you enter a American Protestant church the cross is usually bare and is often represented in a more abstract way, like a cross shaped window. Professor Collins argued that these two different crosses illustrate the two cultures different philosophies about the human body. Catholics are focused on the flesh in all its glory and sinfulness. Protestants prefer to ignore or suppress the body, hiding or ignoring it's sinful and dirty nature.
So while books like "Everybody Poops" may help the next generation to more openly and loudly discuss their gas and bodily functions, I guess I am just an old-school American Protestant kind of lady.