If you pop open your system preferences, open up Keyboard & Mouse, you can set “Full Keyboard Access” to “All Controls. This is massively handy, as you can tab through alert boxes and dialogue boxes, then hit the space bar to activate the selected button.

iTunes, in all dialogue boxes I can test, does not follow the rules here. I seem to have to pick up the mouse in order to get around in the application. At least with respect to alert and dialogue boxes.

You can file your own reports and track them as well. This has been filed as bug #4282397.