Maverick, not sure if you are asking the question to be goofy, or because you honestly don't know. AC3 is audio-only, so it's fairly obvious there is nothing to stretch, but the application has default dialogs. It's simply not sensible to have a different SAVE/RENDER/SAVE AS/OPEN dialog box for each file type, wouldn' tyou agree?
Why do you think that? - If an "option" isn't relevant, then grey it out . . . You have to be thinking of some value in having it remain available. What situation could that be?