I think Wizards actively wants us not to know exactly how the numbers are derived, and I think this thread is the perfect example why. Because most people who post on D&D forums are an opinionated bunch (I include myself in this), and if they knew exactly how a given number were derived, they'd make up their minds on whether it's a good mechanic or not on the spot, before ever running the module, and then they'd just look for conformation when they ran it.
Wizards doesn't want anyone's speculative theorycraft on whether a given system for calculating a stat or leveling up is good or not. They want organic emotional reactions to actually playing the game. They aren't interested in your theory of how fighter damage should be derived. They want to know how the fighter feels when you actually play it. They aren't interested in your speculation that dwarf immunity to poison is overpowered. They'd only be interested if you played a dwarf in the module and for you it felt like a cheap shot when you got poisoned. Yes, "If entire parties of play-testers die at the hands of the Orc, Kobold or Hobgoblin chief, there is a big problem with the play-test." But if after looking at the math and reverse-extrapolating it you think an entire party might die at the hands of the orc chief, that is not a problem, until you actually sit down and play.
Anyway, I freely admit I'm as guilty of this theorycrafting-without-actually-playing as anyone. But I wouldn't criticize Wizards for failing to go out of their way to accommodate my speculation.