Belgium? Seriously? France, Belgium, what's the difference? Nevermind. His nose can still snort the french chuckle. No loss to francophone audiences. And I'm sure Madamme Deneuve won't mind taking short train ride to co-star with him.
The difference is a bilgeload of taxes. Even before the French tax hike, taxes would have been lower for Depardieu if he moved right across the border. (He'd been living near the border even before this spat.) It's no surprise that in a unitary European economy, that those who can live anywhere they wish and work would chose to flee the rapacious French taxes.
However, as the WSJ pointed out earlier this month, this is great news for people who want a little pied-a-terre in France for a second home. If France isn't your primary residence, you aren't subject to these very high income taxes, but those who are leaving don't dare chance the French state insisting that their former primary residence is still their primary residence, so they are selling altogether when they leave (especially if they still have some business interests in France), making it a buyer's market in upscale French property.
So if a 10 million euro estate was out of your reach, but you can afford the 5 million being asked for it now, you're in luck!