what's to stop other languages from
being able to compile down to binary
that runs every bit as fast as C?
Nothing. Modern languages like Java or .NET langs are oriented more on programmer productivity rather than performance. Hardware is cheap now days. Also compilation to intermediate representation gives a lot of bonuses such as security, portability etc. .NET CLR can take advantage of different hardware - for example you don't need to manually optimize/recompile program to use SSE instructions set.
