Coming from upstate NY, I’d always thought that “AdVERtisment” was simply pretentious in America (I’ve only heard ADvertizement from an in-the-flesh human). In Britain, I think AdVERtisment is normal, and probably also in other U.S. regions. However, I’ve only heard it pronounced that way in shows or movies and I live in an educated, upper-middle class town. So I believe that it’s not related to social class or economic standing, but simply geographical, although I wouldn’t be surprised of it varies not by region but by town.