The thing is, he's done the French ground exams. These are not accepted anywhere other than in France, unless there's some kind of exception that I don't know about. Doing a PPL (whether JAA or not) outside of France will mean that he's got to do all the ground exams all over again.
Of course, aerodynamics is pretty much the same in every country, but when it comes to air law there might be a lot of differences, even from one JAA country to another. So re-sitting and passing some of the exams might not be trivial.
For the US, add to this the VISA and TSA hassle, plus the cost of the flight. And, of course, limited choice:
There are however very few schools there which can do a JAA PPL.
There are far more JAA schools in France than in Florida...
Going to the US is a good deal, cost-wise, if you are going to do the full PPL (45 hours plus the rest). But if you're only going there to finish off a PPL, when you've invested 50 hours already, is going to be very expensive.
Weather-wise I doubt whether the South of France is much different from Florida, apart from the occasional hurricane. My guess is that it's perfectly doable to do a full PPL (45 hours and everything) in three-four weeks in the south of France, any season. The reason most participants on this (English) forum don't go to France, Spain or Portugal to do their JAA PPL but to Florida is not because of the weather, but because of the language. (That single flight school in Spain - Jerez - excepted. I'm surprised they are not mentioned all that often on here, but they're probably a great alternative if you want to do an intensive PPL in English. OTOH, it seems from their website as if they're not interested in offering intensive PPL courses.)