Would be very surprised if cocos was any different by design. Or if it couldn't at least be made to behave that way easily via some setup flags.
Yeah, I think what you describe must be what cocos2d-x is doing by default (changing the relevant GL viewport properties based on the resolution of the hardware)
My only question now is what about sprite sheets? If I provide two versions of a sprite sheet image, sprite_sheet.png and email@example.com do I have to provide two versions of the .plist file?