I've also started to notice this with RPGs. I've been banging my head against the Burning Wheel system by Luke Crane for some time now, but keep running out of steam before I've been able to fully digest it. After all, it is a hefty meal of role-playing red meat, bloody and awesome in all its culinary glory. But I love the concepts behind the rules and the way they provide characters with so much additional depth, while abstracting other factors (e.g. equipment lists, which bore me to death these days).
I've been looking for a decent sci fi game to run, as we play very little sci fi in my group (apart from a Rogue Trader mini-campaign), so this week I started reading Burning Empires, which is the sci fi progeny of Burning Wheel. What astonished me is how much clearer it is, and how it makes the entire BW concept easier to understand and to teach others. It then struck me that Empires is really just the Heat to Wheel's LA Takedown. The original ideas are there, but Empires is a much plusher beast, pegged to the sci fi milieu of Christopher Moeller's Iron Empires saga. By sitting down to write Wheel a second time, using a sci fi backdrop, Crane has somehow made the entire system that much clearer.
Of course, there is also the experience of running the game, teaching the game, having others play-test the game, all this goes into putting out a better product. For some authors, this is achieved with a second edition, but frequently such a beast is not a complete re-write, it is often just a cut and paste exercise with new bits added. Empires is a new iteration of the game, written with the benefit of the years in which Burning Wheel has been in print.
Once I got thinking about Burning Wheel, it also struck me that there are a couple of other examples kicking around my shelves. Despite the positive reviews of Spirit of the Century, I've not been able to get my head around it, even though I like its pulp background. I recently bought the FATE core rules, which are a new iteration of the rules engine powering Spirit, and again, hey presto, the writing is much clearer, the explanations so much easier to get your head around. Questions I had about Spirit are readily answered. The door of understanding opens on the library of greater knowledge. Plus, if I get stuck with Spirit, I can always revert back to FATE core for answers.
Another good example is Gumshoe, which when first presented in The Esoterrorists left me scratching my head. Trail of Cthulhu helped shed some light on it, but if you want the best explanation of Gumshoe to date, it has to be Night's Dark Agents. By the time he sat down to write NDA, Kenneth Hite was looking at his fourth shot at refining the Gumshoe rules package (if you count Ashen Stars) and it shows.
Here's a fan trailer of LA Takedown to finish with - those who have seen Heat will notice the obvious similarities: