Indigo, several of those are reasonable questions. Short of turning this thread into a second year macroeconomics lecture, which I'm sure won't earn me any friends (they don't call us dismal scientists for nothing wink ), I'm happy to point you in the direction of this book: it discusses the broad tools required to answer them at a high level. I highly recommend it; it's succinct and well written (I have a copy on my shelf).

http://www.amazon.ca/Macroeconomic-Theory-A-Short-Course/dp/0765611422

For an empirical validation of my first post and initial explanation to you, I'd recommend searching the Federal Reserve site for research on labour market dynamics. They'll have current numbers published across industries with forward-looking estimates and their rationale. You don't have to trust any models to see that different industries and professions have different productivities, requiring a different labour mix, counter to the opinions offered in the linked video.

What is to give light must endure burning.