Good points. It's just that responsive layouts have not been fixed anywhere. Also on the web, it is way too hard. How often don't you see a box floating over some background photo and then covering the focal point, e.g. the face? Sure, it can be done, but the permutations of testing are simply too large for mere mortals.

Multiple 'artboards' for screen sizes/ratios are the solution, which basically just means swapping out a .nib in Interface Builder. Better to just make it explicit.