I'm not sure I believe that is the "norm." And if it is, it certainly should not be.

It doesn't take that much effort (especially now, in the internet age), to learn a little bit about the culture and laws of anyplace that you might want to visit. As such, I have no tolerance, and very little sympathy, for anyone who is too lazy to make that effort.

This subject has been beat to death, which doesn't take much, since it is really quite simple: In French territories service is included. If the service is average then you pay your bill and go. If it is above average then you "round up" the bill, or add a Euro or two. If it is really exceptional then give a little more if you want, but no one will be insulted if you don't.

Is that really so complicated?