Horses: What do They Do?

For some reason, I have been thinking about all the things my mother-in-law said during her visit with us in December. One day we were driving somewhere, she asked what everyone around here did with their horses. We live in Northern Virginia where every other house you pass has some sort of farm animal on it; many with horses. I had to stop and think about that question because I am from northeastern Indiana where most horses that were around us were working horses living on Amish farms. My mother-in-law is from the Detroit area where there are no horses to speak of. Anyway, I really couldn't think of an answer. Around here, the horses seem to live the ideal life. All I have ever seen them do is eat grass in green pastures, run around a little bit, and sometimes run around with someone coaxing them to jump over rails and things. So, what is the purpose of having a horse? It seems to be a really big business around here: equine medicine, equine research, tack shops, etc., but for the life of me, I cannot figure out what the horses do. I told my mother-in-law that they are very expensive pets. People around here can apparently afford them because everyone (except us of course) has one or two or a bunch. Maybe if the price of gasoline prices keep going up, they will be employed as transportation!