It was inevitable, in retrospect, that magic would go all over. And that's not even counting the influence of fantasy fiction, movies, comics and especially anime, where the current generation of gamers are seeing ubiquitous magic as just the way fantasy looks and feels. Appendix N includes a lot of stuff modern gamers have never read and may even find almost impossible to get their hands on.
The excellent Magical Medieval Society: Western Europe book shows it can be done, but it does require some elbow grease to make it all fit together even somewhat plausibly.Part of the problem is layering it onto a pseudo-medieval or pseudo-classical setting. You have to lay on the fantastic really thick because medieval (or classical, or renaissance) is the opposite of fantastic; it's dismal and inferior