One of the report's main conclusions is that the majority of medical errors do not result from individual recklessness or the actions of a particular group--this is not a "bad apple" problem. More commonly, errors are caused by faulty systems, processes, and conditions that lead people to make mistakes or fail to prevent them.
In your example above with the wrong dosing, don't forget that there is a chain of people that that dose goes through -- e.g. the pharmacist, the nurse, etc...It is their jobs as well to question medication. In fact, nurses will state that if a wrong medication is given, then they are liable for it, even if the doctor ordered it (this is anecdotal, I do not know exact policies and procedures around this). Of course, people will argue that if nurses question a doctor they will never win. And while this argument is appealing to our preconceived notions of power structures and roles, the reality is different and there are procedures to escalate issues such as this. Again, this is to underscore that medical errors are mostly due multiple failures in the system or deficiencies in the system itself. Let's face it -- to expect perfection from one person (a doctor, a priest, the president, you name it) is unreasonable at best and irrational at worst.