That had to be the criteria to give it to zenyatta the year she 'won' it. She never beat an open company field that year and was still awarded HOY despite losing head-to-head to the horse who deserved it. That award was rendered meaningless to me after that.
I felt the same way when Julia Roberts in Erin Brockovich beat Ellen Burstyn in Requiem for a Dream for the Best Actress Oscar.