Seriously, you can get great photos with a cheaper camera. There are many options and a 300 or 400 mm zoom will do fine.
The only problems will be, if you want to have large prints like posters, which is probably not the case.
action shots, a good slr camera with a zoom lense is ok when they are not moving too much, but if you want to shoot multiple times (to pick the right one) while they are hitting the ball, then the quality won't be that good unless you use a high speed telephoto (not zoom) lense, which are awfully expensive (more than the cameras themselves) and you need a camera to match.
Said that, I don't believe most sports photographers have a camera like this one, it's really the top of the line (of any camera). They do have the lenses though, an 600 mm is about $10,000.