So how many iPhones...
.. have been sold in France?
Divide the number of exploding iPhones by those bought/in use. Multiply by 100 to get the percentage - if it's miniscule then it's hardly of major concern. I suspect it'll be way, way below the level of returns to any major supermarket on a daily basis.
How many TVs, radios, MP3 players liquidate themselves in a heated fashion? How many people set fire to their houses and selves by smoking? What is the exact risk of death/injury by iPhone compared to any other daily risk?
It's a problem, for Apple, and the users. But they need to investigate it and fix it.