Actually the big advantage is any SLR (digital or film) for shooting sports, action, and things in motion is the fact they have a mechanical shutter and when you push the shutter release there is no appriciable delay in from pushing the button to actually taking the picture. Most digital point and shoots have an 'electronic' shutter where there is a delay from when you push the button to when the image is recorded.
For example, say you were trying to take a picture of a fish jumping clear of the water. You see the fish jump, and push the shutter button while the fish is in midair. A point and shoot will typically delay so much that the image is only going to be recorded after the fish falls back into the water leaving you with only a nice picture of a splash. In the exact same scenerio, the SLR camera is going to give you a picture of the fish in midair at the instant you push the button. Use that same analogy with crossing a finish line, catching a football, a baseball swing, etc... and you will soon see that a SLR is the ONLY way to shoot sports photos. the 'D' in DSLR only refers to 'digital' which is just a matter of preference over film, the important part for sports is the 'SLR' which stands for single lens reflex camera.
The speed of the lens is just photospeak for how much light it lets into the front end of the lens. More light means you can shoot the picture at a higher shutter speed, the higher shutter speed reduces motion blur. A shutter speed 1/500 of a second will freeze pretty much anything. For outdoor sports a lens that opens up to f/3.5 is dandy, and f4.5 will work. For indoor sports you really need a lens that is f/2.8 in my expierience. As that 'f' number fets smaller, the lens gets bigger, heavier, and more expensive.
- Brad