I think what really makes the pictures you linked to remarkable are the moments that are captured and the composition. Pay attention to the angles and how he crops the photos. When he includes the background, it directly contributes to the photo. He's also obviously scouted out his locations to get in the right position for the angles he's gotten. You can see some of the same things in DC Fan's photos, especially how his photos are portrayed. It looks like he's shooting an enduro or XC event, which is all about pushing past the normal limits of endurance. That's shown in the facial expression of the first rider, and the mud-spattered intensity of the second (OK, they're both mud-spattered). Mr. Valentine is obviously showing intensity and high-paced action. . .even in his portrait of the women in the wedding dress (which I love).
Now, as for the sharpness and color saturation, some of that does just come down to the right equipment. That's not to say you can't achieve very good results with the equipment you have, though, especially with the correct post processing. But it all starts with the basics. Use the right shutter speed to either freeze or blur the action in the way you intend. Pay attention to the light. If you can use artificial lighting, that gives you the ultimate control, but usually you're working with natural lighting, so pay attention to that light when you're picking your location. Speaking of location, being a rider yourself is going to help, because you need to figure a few things out. Where is the action going to take place? What elements best illustrate this action (both elements of the rider and his/her background)? And lastly, where do you need to position yourself to bring all of this together? Now, I'll admit having a camera that can shoot 10 fps and a zoom lens that can pick out the beeds of sweat on the rider's eyebrows from 100 meters away certainly helps, if you can nail those technical and artistic elements, people are going to be too busy saying "Wow, what a shot!" to worry about what camera/lens combination you used to get it.