I think the use of an invisible identifier to label the mapping between a file and it's app is a really non-intuitive interface. Getting rid of files without extensions and making it dead simple to know what will happen if you open a file improve the experience, even if it seems backwards, clunky, or non-sophisticated. I think this change is a really mature decision on Apple's part even if it isn't the traditional Mac way of doing things.
It used to be the case that the file's icon represented the file's type. But with icon previews, that's no longer the case, so the extension is the only visible means of conveying the file type.
