Can't tab between dialog options on Finder's Replace File dialog
Looks like another example of Apples notoriously great user interface. In order to use keyboard to interact with the dialog, you have to click on it first.  But it has to be on the text of the question, not the title bar or blank grey areas around it.

When the dialog is activated, it's the focused window.  You can tell by looking in the Window menu.  The "Copy" window has checkbox next to it.  But it's in this magical-apple-great-interfacy focused state.  In order to make it focused proper, you have to click on the text. Oh, also, like all great UI's, it will not give you a visual cue that it went from apple-magical-focus to normal focus.  But if you press tab, the buttons become selected in a rotation.

The only solution I can think of involves Apple's wonderfully user friendly and clever programming language AppleScript.  Or some automation tool like Keyboard Maestro.  Or skip Finder all together for an option that's less magical like Terminal or ForkLift.

PS Sorry about all the sarcasm.  It's just the only thing that annoys me more than Apples awful UI's is their marketing boasting how user-friendliness is their forte.