I whined about not being able to manipulate modal dialogs without my mouse and one of my friends, Tom R., pointed out how to get OSX to behave as I had hoped. The trick? A System Preferences change:
- System Preferences
- Keyboard
- Keyboard Shortcuts
- Keyboard & Text Input
- Full Keyboard Access: All controls.
- Keyboard & Text Input
- Keyboard Shortcuts
- Keyboard
Programmer, husband, father, singer, guitarist, tinkerer, reverse engineer, strange, and living in New Jersey. 
Glad to be of service.
Now. Apple doesn’t leave this as the default… why?
Drives me crazy, too. You will find there are still things you can’t do with the keyboard. Not good, but such is life.
I suspect, as someone mentioned on FB, that it’s a “security” feature – how many times have you been typing and all of a sudden a modal dialog pops up and grabs focus and you press enter selecting the default action?
I think the right “answer” is to not let modal dialogs grab focus, but bind a well-known keyboard sequence to move focus to a modal dialog is the best solution here.
The default being that you cannot use the keyboard at all to manipulate a modal dialog box is just epic fail, however.
Short & Sweet, thank you!