They're different tools for different jobs. Lightroom is an image manager and raw editor. Photoshop is an image editor with a raw editor plugin. Both use Adobe camera raw (different versions of ACR for different versions of PS/LR though) for raw editing, but it's a native component of LR and easier to use in that program with a few features that PS doesn't have.
Have a look at the manage, develop and perfect, and present sections here:
http://www.adobe.com/products/photoshop/family/prosolutions/