In some of the package managers I studied, applications co-exist with libraries and plug-ins. In package managers that provided no clear distinction between the two, like Synaptic Package Manager and Puppy Package Manager, users were often unable to distinguish based on the title and descriptions alone.
Some of the package managers, such as Ubuntu Software Center, showed an icon in the list of packages. Not all of the packages had an icon specified, and used the default. Although this method does not necessarily distinguish between applications and other packages, in practice graphical applications almost always had their own icon, while other packages did not.
The test users were looking for graphical applications, and found the visual clue very useful. In Synaptic Package Manager, many of the users installed libraries or command-line tools because they could not tell based on the title and description alone whether or not the package was a graphical application. In Ubuntu Software Center, none of the test users had that problem. Supporting package icons provides a simple method of improving users’ ability to select the packages they want from the many irrelevant options in the same category or set of search results.
Brendon Robinson's Blog 