While Photoshop+Bridge generally offer the same capabilities, Lightroom is packaged and designed in such a way that all those capabilities are far more accessible. In Photoshop, you don't have at-hand access to the histogram, tone curve, white-balance (color balance), and exposure tools all at once. There are a wide variety of other photography-related tools that are also available at your fingertips in Lightroom, where as the same tools or operations may require a sequence of activities to find and use in Photoshop. Some tools offer capabilities that are not found in Photoshop, like the new camera lens profiles of Lightroom 3.
Workflow is better with Lightroom, as your library management and development are all in a single application. You don't have to switch back and forth, and many library-management activities can be performed from Lighroom film strip on demand. Additionally, Lightroom provides to additional workflows for generating web sites and slide shows, as well as a very rich workflow for print management. The printing capabilities of Lightroom are pretty extensive now in version 3, providing tools to print booklets with multiple prints per page in artistic layouts very easily.
Overall, for a cheaper product, Lightroom really outshines Photoshop as far as digital photo editing goes, despite the fact that both tools offer the same capabilities. Lightroom just makes it a whole lot easier and quicker.