I think we may be having different definitions of a game being integrated into its setting and/or genre. Could you take the core mechanic of d10+stat+skill vs difficulty, along with mechanics for damage and such and build another game around it? Sure. You could bring along the magic system, though it does have a bunch of medievalisms in it as well (such as not being able to affect anything beyond the Earth). But skills, advantages/flaws, creatures, and all that other stuff that makes it a game rather than a game engine, all form around a medieval core.
To use a D&D analogue: D&D is built around a setting that vaguely corresponds to Greyhawk. You have studious wizards, you have clerics wielding both martial implements and divine magic, and there's a huge gaggle of various monsters with different roles in the world. You might be playing in Greyhawk, or the Forgotten Realms, or Eberron, or a homebrew setting, but they're all essentially Greyhawk with different geography. If you want to change a lot of the built-in Greyhawkisms, you could get something like Arcana Evolved, with mostly the same rules engine but different races, different classes, different spell lists (both in the actual spells and in how they're organized), and so on. Or if you want to go to another genre, you'd get something like d20 Modern or one of the d20 Star Warses. They're all built on the same core chassis, but they're also very clearly different games.
That's basically how I see using Ars Magica outside of Mythic Europe. You can certainly transplant the game to a different geography, where things like Provence or England doesn't exist, without other consequences than you having to make up more material yourself. But that would be the equivalent of setting your D&D game in Greyhawk instead of the Forgotten Realms.
