Icons that can be used for the development of open source projects, themes and plugins are very rare. So many designers are either a little lax in their licensing, or opt to use creative commons licenses.
Icons Increase Clickthrough Rate
I use quite a lot of screenshots when blogging as I find the old saying “A picture is worth a thousand words” very appropriate.
Michel Fortin also pointed out in his top plugins and blogging tips article today how graphic icons with each post help with clickthrough. He has been using eye tracking software to prove it, and is a fanatical tester.