Yes, dragging & dropping / extracting are synonymous.
Generally speaking, media type files don't compress much.
Why don't some files compress very much?
Some types of files compress better than others. For example, most multimedia files already exist in a highly compressed state. The standards for these file types usually specify efficient techniques to compress the data they contain. Examples include, but are not limited to, graphic (picture) files (GIF, JPG, etc), music files (MP3, WMA, etc), and movie files (AVI, MPG, etc). Once a file has been compressed, it usually cannot be compressed more to any significant extent. Therefore, such files don't get much, if any, smaller when they are added to a Zip file (.zip or .zipx).
Also, the _MACOSX file is just for apple's indexing, it allows Apple computers (the one it was packaged on) to search the archive's contents quickly (without having to unarchive it). At least from what I can tell.