I say that if a LION (Christian the Lion, to be specific) can run up to his previous humans and show obvious affection for them, after a year of being left in the wild, why can't a horse love their owner?
Security, food, warmth/shelter... That's what you give a horse. And sometimes, if they don't have a pasture mate, company. I have a horse that was SO attached to dog that the family owned, because he didn't have a pasture mate. The dog returned the affection. When the dog got hit by a car, they brought it in the house to tend to it. It wanted to go outside with the horse (it'd go to the horse's shed). Finally, they compromised and brought the horse into the garage. The horse stayed with the dog until it healed, and both were calm during the ordeal.
I think that animal's can show us that they have feelings if we let them. Just look at those videos of that elephant painting other elephants. Elephants holding flowers, mother elephants walking with their babies, etc. Not everything an animal does has to be based on instinct.
While I don't want to get off topic on religious views, I truly believed that we evolved from primates. (Whether or not that was caused by an outside force is YOUR choice to believe or not believe.) In that case, we were once animals too. And we can love, so why can't they?