On one side, I don't understand your opinion : sport is about sportsmanship. As a fan, I wouldn't like someone who would insult his opponents and trick them, even if he had multiple WRs.
On the other hand, unlike the amateurs who worry about their times, a pro marathoner must worry about both his time (prestige and sponsoring) and his placement (reward). He couldn't just slow down to annoy the drafter, else he sacrificed the first, but it would be cruel to lose against someone that way. And keep in mind that a whole family and community might live from the income of that one runner.
Oh, but same thing goes for the drafter, so I guess I will stick to sportsmanship...