If you do this from the beginning, it is not a big deal: and in fact, it really helps save you time later when things change. It simply is not difficult to compute a layout rather than drawing one in MS Paint... I mean, even Xcode's Interface Builder solves this problem quite well... I frankly am surprised so many people are disagreeing with this "aspect ratio" bullet point, given that if you take a random non-game app from the App Store and change its aspect ratio it is almost always going to do this correctly: Apple makes it hard to screw this one up. ;P
If you have to design for arbitrary resolutions and aspects, you are way more limited in what you can do with your design. On a touch device this is even more severe because buttons that are too narrow will be hard to reach etc.
Also, if you are not using standard controls and you have a designer make a couple of images for you, you will now have to split those up into parts to render your UI. It seems that you would argue that this is the only way to go but surely we can agree that it is more expensive for the developer?
