- Education/Licensing Barriers -
A lot of high paying jobs have certain educational requirements that discourage and/or prevent a large percentage of people from trying to enter certain careers, such as doctors (Med School), lawyers (Law School), dentists (Dental School), veterinarians (Vet Schools), pharmacists (Pharmacy School) and professors (PhD). I'm sure there are a lot of people that would love to become doctors, lawyers, etc..., but don't have the time, money, intelligence, work ethic, etc...to attain the necessary educational requirements/licensing requirements.
In general, the more education you obtain, the more you get paid. You get paid more because it is assumed that because of your additional educational attainment, you have more knowledge on the subject and can utilize that knowledge to become a better employee.
- Undesirable/Dangerous -
Another reason that some jobs are paid more than others is simple economics. Jobs that are dangerous tend to be higher paying to offset the fact that the job is dangerous. People don't want to work a dangerous job, so if there's a shortage of workers, more money has to be offered to lure workers. Basically, workers are getting paid more to try to make up for the fact that they could get very seriously injured or could even possibly die on the job. Examples of this would be loggers and fisherman. (< First examples that came to mind)
- Long Hours and High Stress -
Investment banking is a good example of a job that has long hours and high stress. A lot of people want (or at least wanted) to get into the investment banking industry because the pay is ridiculously nice (100k for recent college grads). If the pay weren't so good, there's no way so many Ivy League grads would dream of working a job where you work anywhere from 60 to 90 hours a week and have very little semblance of a social life. I'm sure there are some people that somehow actually enjoy investment banking, but the majority do it for the money and exit opportunities, i.e. hedge funds, private equity, venture capital, etc...
- Responsibilities -
Whenever you get promoted, you usually take on more responsibilities, and your pay increase is compensation for the additional work you have to do. This is why Target managers get paid more than Target sales clerks.
One of the reasons anesthesiologists are paid more then orthopedics is the fact that anesthesiologists have a much greater impact on whether a patient lives or dies than an orthopedic. Not that I'm bashing orthopedics, but they just aren't as responsible for the lives of their patients as anesthesiologists. If an anesthesiologist messes up during surgery, someone could very easily die, whereas with an orthopedic, it is very, very unlikely that they could have such a grim effect if they mess up.