Lightroom and Aperture are designed in a way to make the workflow of a photographer after taking a shot.
So at first you import the pictures into its library. Much like iPhoto, but much more powerful. You can do tagging, collections and such. iPhoto has its uses as a family picture repository, but Lightroom is for storing all your stock images.
Then you have to do the developing. Here you can adjust virtually every aspect of the image and it is all done in a way as to keep the picture in focus. Seriously, I'm not just talking here. It is all focused on your images.
Then of course there's options for exporting, web galleries, printing and such in the following steps.
The best part is, your original image is untouched. All the editing is non-destructive. So if you adjust the brightness to +20, you can always reduce it back to zero. There's no "Apply settings" which makes a permanent change to your image. So every time you view the image, the settings are applied in real time.
Photoshop of course has its purpose, that is, image editing. It should be used to produce one final image while lightroom is for your entire collection of digital photos....
Sound like a salesman? I am!