Speed Of Light or Maximum Observable Velocity, Part I

This is my birthday Blog so I figured I'd make it a good one. I recommend a handful of tasty Triscuits to go along with this post.
I've always had a hard time dealing with the absolute speed of light. I enjoy that the value c (Speed of light = 299,792,458m/s) has lent a helpful hand in so many of modern science's most useful equations. Equations formulated by Maxwell, Einstein and Lorentz all rely on the constant speed of light. Even one of the most famous equations of them all, E=mc^2 (pronounced, "e" equals em sea squared) uses the constant speed of light to help us better explain or understand the universe around us. Incredible! But what has always been most incredible is that the speed of light is constant. Not only can you not speed it up greater than c, such as shining a light from a moving train in the direction the train is moving,,, but you also CAN'T SLOW IT DOWN to less than c, such as shining a light from a moving train in the opposite direction. It is constant, can't change it, observable truth has proven it, and the BIGGEST of big-time scientists have used it to prove what they had faith in most.
Do you understand what I'm saying and why I see this as completely wild and mildly unacceptable? When I sit on a train moving at 60mph and I throw the pit of my apricot at 40mph towards my future destination, a static (not moving) observer on the near-by bluff will witness my pit flying through the air at 100mph (assuming zero wind resistance). But if I do this EXACT same thing replacing my apricot pit with a beam of light, the static observer will not witness the light beam moving at c+60mph; the static observer will witness your regular old run of the mill (constant speed) beam of light traveling at c. UNCHANGED, even though it was being changed just like the apricot pit.
Now due to this conundrum I can't sleep at night and I find myself constantly asking why an apricot pit behaves so fundamentally different from a beam of light? Furthermore, why is the speed of light an important factor of E=mc^2? c is not subjective, it is very much only (and always) 299,792,458m/s which is, indisputably, only the speed of light (in a vacuum). So I understand how the number 299,792,458 squared, then multiplied by a mass in kilograms results in a large number of x kilogram meters^2/sec^2 (or Joules), which is an amount of energy (E). So the number and the units make sense,,, but why does it have to be the speed of light. Why can't c be the speed of a HELL OF fast jet plane in m/s? Or the speed of the Earth in m/s? Why does light have anything to do with this? Part II coming soon, like tomorrow! I'm so 28 right now.