c) there's nothing preventing you from shipping a zip (because windows still doesn't understand a tarball) which has everything packaged up nice and neat (ie, a bundle)
It seems you don't completely understand what an app bundle in OS X is. Yes, it is a directory where all the files that comprise an app are packaged up nice and neat.
But that directory is treated by the Finder in a special way: from the point of view of an end user, it is just a file. He double clicks on it, and the app launches. He drags a document icon on top of it, and the document opens in the app. He can move it around, move it to another disk or to another Mac, etc., and it consistently behaves like a single file and retains its functionality. Only when he right-clicks on it and chooses "Show Package Contents" is its true identity as a neatly organized folder revealed.
In fact, app bundles aren't the only kind of packages (i.e., directories that present themselves as files) in OS X. There are many others. For example, some apps like Apple's Keynote save documents as packages. From the point of view of most users, a Keynote file is pretty much like a PowerPoint file, except for the app that opens it. A slightly more advanced user knows that he can right click on the Keynote file, search for the graphs he included in the presentation, and replace those files (PNG, JPEG, PDF, whatever) with updated versions that reflect updated data... and the presentation gets updated without even opening Keynote.