Corruption is actually against the core interests of those people who are in power. Think this way, they kind of own the whole country, why do they want to be corrupted for? However when the other people who are under their control are corrupted, then it will cause a lot of problem for the leaders, because those corruptions will just mean that they are loosing control of that is rightfully theirs. Of course this doesn't mean nepotism is not in play in China, but this is already rooted in the East Asian cultures, and it will not be eliminated by any systems.
Let me make another analogy here. Think of a company, who do you think will care more about the well being of the company and are more resentful towards corruption within the company? The people who owns the company or some hired executives?