Those ZIP-archives (and others) are surely useless, once unpacked. So why they aren’t moved to the bin by default, I do not know. However, here’s how to set things right: Just click on “Go” in the menu bar, then “Go to Folder…” and type in System/Library/CoreServices. Now open the Archive Utility and check out the preference settings of the app in question. In the settings you can opt for: After expanding: move archive to Trash. That’s it, one less thing to take care of on your Mac.