Actually iPhoto and Aperture's storage features are not the same. While with the current release of each application they share a common library structure Aperture gives you a much richer set of features to manage your collection. This especially comes into play on a large library. Aperture is clearly better at managing the library.
Aperture's image adjustment and development tools are far superior to iPhoto's especially if you shoot RAW.
Aperture isn't an editor in the sense of a PS. Aperture is a digital image developer, it develops the digital images much like a darkroom develops film negatives. Aperture doesn't do the type of cutting and pasting that a program like PS does. What it does do is give you the tools you need to take an image from the camera to the final print.
Many users of Aperture also make use of an editor like PS or GIMP from time to time in their workflow. Aperture gives you the ability to hook one of these programs into your workflow so that an image can be worked on in Aperture sent to PS and then returned to Aperture for further development and storage.