Not in the real world.
1. Like in any organization, the boss exploits the workers he doesn't like more than those he likes. Who he likes might be based a random factor like sense of humor/gender than ability.
2. People rarely drop out of phd programs (single digit percentage at most in my experience) because they don't want to fail. So, in actuality, the drop out rate difference exploitative advisors and good ones is too small to be significant.
3. Somewhat contrary to point 1., passionate students are usually better than uninspired students, and so passionate students usually have more leverage than the uninspired. They can switch advisors or schools - making the advisor look bad. In my experience the exploited ones are usually those who are in the bottom half of ability.
4. Its very difficult for advisors to "fire" a student usually. It reflects badly on them, and they usually have to go through a painful review process with the university to explain why the student was asked to leave. Therefore, advisors will usually treat horribly the students they don't like so they leave on their own accord.