Just a force of habit I guess, you have to do it the hard way if you're working with spritesheets and such. And sometimes you might want a different name than the file name. I almost never drag & drop myself, but it sure is faster and easier if you name your images properly. As for the video tutorials, you have to show people how to do it the proper way first at least. It's a great feature though, so it should be mentioned.
Edit: By the way, this topic should probably not be in this sub-forum, it's not exactly a question of how you do something.