If I have understood it correctly, PPAs are still the only way to publish free, open source apps for desktop Ubuntu.
However, especially new users install applications only via Software Center and the applications using PPAs are not visible to the users at all. They are not being found.
Microsoft has a concept in which desktop application vendors are able to submit only a link page to their desktop application. This means that the application is listed and can be found in Windows Store, but the store just redirects the user to an external download page. A similar concept could be applied to Ubuntu Software Center and PPAs.
For more info, see:
http://msdn.microsoft.com/en-us/library/windows/desktop/dn374786%28v=vs.85%29.aspx
ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: software-center 13.10-0ubuntu4.1
ProcVersionSignature: Ubuntu 3.13.0-34.60-generic 3.13.11.4
Uname: Linux 3.13.0-34-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.14.1-0ubuntu3.6
Architecture: amd64
CurrentDesktop: Unity
Date: Mon Jan 12 00:02:57 2015
PackageArchitecture: all
SourcePackage: software-center
UpgradeStatus: No upgrade log present (probably fresh install)
PPAs, like any apt software archive, can replace any package on your system. For example, a PPA maintainer could replace your kernel with one that doesn't boot, or replace Xorg with a version that includes a keylogger and sends your credit card details to Eastern Gabistan. That's why we don't provide PPA discovery in USC, or promote PPAs as a method of publishing software for end users. If you do add a PPA, its packages become visible in USC, and it's added as an item in the "All Software" menu, but that's as far as we go.
Fortunately, it is not correct that PPAs are the only way to publish free open-source apps. Since 2011 you have been able to use the MyApps system for that. <https:/