There are a lot of questions in there - mostly ones I am not qualified to answer. But for this last one:
what's to stop other languages from being able to compile down to binary that runs every bit as fast as C?
In a word, Abstraction.
C is only one or 2 levels of abstraction away from machine language. Java and the .Net languages are at a minimum 3 levels of abstraction away from assembler. I'm not sure about Python and Ruby.
Typically, the more programmer toys (complex data types, etc.), the further you are from machine language and the more translation has to be done.
I'm off here and there but that's the basic gist.
Update ------- There are some good comments on this post with more details.
