Very interesting question. Have never really thought about that but yea most stories with magical Worlds are pretty medieval looking.
Can we name any movies, novels, tvshows etc that have a modern type World where there is magic?? I sure cant think of any right now..
Imagining what such a World would be like I agree with Spoekenkieker that religion would still play as big a part as it does now if not actually an even bigger part. The presence of magic would, I think, put in a certain kind of chaotic aspect to the World, if some people could change the wheather for instance too their own liking or something like that, that would in some sence mess with the universal order of Things wouldnt it? And so the regular people would turn to faith even more then in our World.
I imagine some of the Technologies we have would be replaced with magic ones because that would be easier, like lamps and lights. Tv’s and communicational devices. Its hard to imagine really what such a World would be, maybe we would have all gone insanly powerhungry and most likely blown up the World long time ago… come to think of it perhabs thats why they never get any further than the medieval times 🙂