The bridegroom is considered the most important person in the marriage procession since it is his marriage. Thus he sort of gets the honour of having an entire vehicle to himself, whether it is a motorized one or one which is harnessed or he may even be seated on a horse. However, it is not entirely correct to say that he will be starting out on dealing with a new aspect of his life solely on his own, tackling all challenges alone. Maybe in a certain sense he is starting his own independent family life and is the main support of his bride. Yet, his family will continue to be his support system too when needed and they will also be responsible for ensuring that his new life partner is well cared for in their midst. In this sense, the people in the procession, who are generally close relatives other than a few friends, are an indicator of that support system - they are there along the way ahead.
What Dr. Srinivasa said too makes sense - identifying who is the groom can be a puzzle, what with everyone dressed in finery. Besides, even turbans are no longer the sole prerogative of the groom, with all family members too sporting the head gear. So when we see the person on the horse or in the decorated car, we will know it is the groom - provided, of course, the groom himself is not also enjoying himself, dancing along with his family & friends and somebody else is seated in the car!!
When people come at you with their worst, you should come at them with your best (advice given to Selena Gomez by her mother, quoted in Time magazine.)