IMO you forgot to mention one of the most important differences between Aperture/Lightroom and the rest of the apps, as iPhoto, PSE, PS3, CS3 etc.: Aperture and Lightroom will NEVER change your original photos when you are editing them. AP and LR just keep the originals plus save the editing commands. AP/LR will render the pictures at any time you want to look at it, print/export it (that is why you need a better GPU etc).
Even if you export your picture from Aperture/Lightroom for more sophisticated editing to PSE or PS it will be returned automatically to AP/LR by PSE/PS just by saving the edited (psd, tiff, jpg ...) version in PSE/PS, but within AP/LR there is still the original (raw or jpg) photo to which the edited version will be attached. Therefore you can allways got back to square one. If you try the same with e.g. iPhoto, your original file will be overwritten by the edited picture and you have to be happy with your edited version. No way back.
BTW PSE and PS have one major difference, that might even be of interest for those of us would don't need the very advanced editing power of PS: With PS you can edit (nearly) everything in 16 bit mode, whereas PSE offers 16 bit mode only for that kind of editing you can do anyway in Aperture or Lightroom. For more advanced features you have to switch to 8 bit mode in PSE.