I agree the description is a little unfair, but the point is sound.
This is how it should work
1. User clicks download link
2. Browser downloads a standard cross-platform .zip file, decompresses in a temporary directory
3. Browser notifies OS.
4. OS looks in Info.plist for instructions on where to install, possibly mpkg for more complex installers
5. OS prompts user for permission to install and possibly run the app, or passes user over to Installer.app for complex installs
6. Temporary files are deleted
From the user's perspective it would work like this
This is how it should work
From the user's perspective it would work like this