When I download zipped files on my Mac using Safari, the zipped file is placed into the Downloads folder and is not unzipped. If however, you click on the zip file (which will look like a folder), then it is automatically unzipped and the contents are available in Finder, under the zip file name. Caveat: I am running the latest version of OSX, and I believe the auto unzipping occurred in an older version of the O/S or Safari, according to Preferences settings.