I never played 1st, mind you, so I can't comment on that.

A lot of the rules in second edition were apparent fiats. I imagine that through countless hours of hands-on experience, they found what worked best and I just had to trust that they were right. And they largely worked, I have great memories of games I played in second edition. I think the complete insanity behind the system actually helped shape the way we played our games - if the DM didn't know how to adjudicate on something, he just pulled out a judgment relying solely on his best guess based on past experience. And that felt fairly natural, since I'm pretty sure every other rule in the book was made the same way.

With later editions, there was a far clearer, unifying mechanic to the game. Just understanding the d20 vs. difficulty check roll will allow you to resolve most situations in the d20 system, the DM just has to decide what variable best measure the conflict.