They want to purchase the French layout because the laptop may last longer than you do with the company (smile). In such case, they'd have to return it to the office pool, and who'd want to use it, if everyone there is used to the French-layout keyboards????
The IT director probably doesn't want to get stuck with a useless piece of equipment -- nor would I. But see, you (or the company) can always purchase an external US USB keyboard and use that. A decent one could be had for 20-30 USD. This would be a good compromise.
Insisting, on the other hand, might not put you in a favorable light and might be considered as rude.