In jobs today, being an expert at solely one thing is never a good thing. Being moderately good at various things proves to be useful in many -- if not all professions. People look for those who are well versed in their field based on many, many aspects that they wouldn't have if they were merely a Master of One. In all, I'd rather be a JoAT than a Master of One.
Sweg.
You got any examples of these jobs? The jobs that I know of require practically one train of thought and nothing else. It's not like there are many jobs out there (that I know of) which require some knowledge of EEing in addition to a Biologist's encyclopedia. :I
Trick question, master of all trades is te only true answer.