This is also why it's so hard to meaningfully come up with something novel by thinking really really hard about it in a secluded cave. You need to refine your ideas by constantly testing them in the market of ideas either through collaboration or concrete implementation.
It's hard to get into, but the systems it implements compliment each other really well to create a realistic space empire building game.
Examples you mentioned above are all "mass market" (except DF) in comparison.
I don't mean to diminish the work of Crawford, but he is building the same kind of simulationst mechanisms that Adams is, but Adams hit on success partly because of his personality.
It's almost perfectly the academic/amateur divide if you will; which is amusing given Adams' background in education.