Islowry, I'd like you to sit on my horse and see her perform a dressage test. Or in fact get her to just walk in a straight line.
People who criticise Zara Phillips (and, in the past, Princess Anne) , saying that they only got where they are because they have the money to buy the right horses simply don't know how much is involved in succeeding in equestrian sports. Yes, it is true, having money enables someone to buy a good horse. But from their the rider needs the talent, the patience, the nerves and the dedication to succeed. Even a dressage rider needs these things - although no scary fences are involved in dressage, it still needs courage and confidence to sit on a fit horse, no matter how well schooled, and get a good performance out of it. And ask any first time rider how they feel the day after they get on a horse and they will tell you there are muscles involved that they never knew they had. Riding involves a partnership between the rider and the horse.