Dan Moren reporting on Amazon’s recently released Mac Software Downloads site:
This is where the process gets quite a bit less convenient than buying through the Mac App Store. The first thing you actually download is a small disk image (2.1MB in size, in my case) containing an application-specific [Software Name] Downloader program. Open this disk image, if your browser doesn’t mount the image automatically, and double-click the Amazon Software Downloader.app inside. After a few seconds, the Downloader program begins downloading the purchased software—not to your Downloads folder, or even to your Applications folder, but to a new folder on your Desktop.
Doesn’t sound like the best user experience. However, if an application you’d like to purchase isn’t available in the Mac App Store, Amazon’s Software Downloads is a nice second option.