First, things like health care and free university are a huge deal if you plan to stay past your 30's. Consider being able to take a couple years to try a business without freaking out about health insurance. Consider being able to go get a PhD in some interesting subject without having to get a full scholarship. Consider, obviously, having kids and sending them to world-class universities without incurring any debt.
Then there's the job security aspect. It can be really nice to be employed in a country where people aren't just laid off whenever a company misses its quarterly numbers.
And finally, if you really are an actual Expert in a field where that's worth a lot of money, it's probably worth about as much in France as it is elsewhere. Sure all the "senior" programmers with 3 years' experience get paid a lot less than in the US, but I don't think the VP level does badly at all.
(Maybe I'm being naive here... my point of reference being Germany.)
I hear it can be very hard to get a proper, "permanent" job in France, but I also hear the quality of life is pretty amazing if you do.