There is a very large difference between a specific mobile design and a site that is viewable using a mobile device. For example, most websites are viewable using an iPhone or iPad, but not ideal. As long as flash has not been used to create the navigation or show images, people surfing a site using these devices should be able to navigate around and eventually find what they are looking for.
Mobile design on the other hand is the practise of analyzing what customers and potential customers will be looking for on specific website while using a mobile devices. If it is a hotel, the viewer is likely looking at rooms, prices and contact information. If it s a real estate agent, the user is likely looking at the home inventory and contact information. As you can see, it is really the process of determining who the audience is and how best to "serve" them up your information in the most effective, user friendly way.