Have a look at the 4e PHB rules on powers. We have six pages to define and explain the concept of powers, but dozens and dozens of pages listing powers. For me, that's six pages of rules and gazillions of pages of data to be processed using the rules. Did anyone actually have a fun time devouring all those powers?
I wouldn't say I had a fun time devouring all those powers. But from time to time I do pick up the PHB, or a power book, and look through the lists of powers to get ideas about what I might do in the game.
Similarly with Monster Manuals. I see these lists of rules elements as the source of inspiration for adventure design. Although they are just mechanics, I find it fairly easy, when reading them, to imagine them as mechanics-in-play.
I'm also surprised at how many people enjoy the sample of play excerpts. I see them as useful and often necessary, but rarely fun to read.
I don't mind reading them, but often they are a lot less helpful than they could be.
Two examples:
In the Rules Compendium (4essentials), there is an example of a skill challenge. The skill challenge ends with the players failing. In resolving that failure, the GM does so in a
metagame fashion - that is, the GM determines the consequence for failure not by extrapolating from what went wrong, in the fiction, with the last attempted skill check, but rather by deciding on a consequence that is suggested by the earlier play of the encounter, and which makes sense as a way of bringing to an end the PCs' attempts to unravel the challenge.
Now I have nothing against this way of GMing. In fact, in my view, without it you can't make skill challenges work. But nowhere do the rulebooks talk about how you might do it! Nor is there any commentary on the example of play that explains what the GM did. It is all left as an exercise for the reader. In my view, that is a crappy way to explain the rules of your game.
Second example: in Burning Wheel, players and the GM have to script their combat rounds in advance, with only a limited capacity to change manoeuvres once the scripts are declared. Now, Burning Wheel melee also has parry/dodge rules, but if you don't script your parry/dodge at the same time as your enemy scripts his/her attack, then you lose! So being lucky and clever in your scripting is an important thing.
But in all the examples of play in the book, the opponents "just happen" to script their attacks and parries/dodges simultaneously. So (i) we get no example of how to resolve an attack where there is no scripted defence, and (ii) we get no example of the fizzling of a defence when there is no scripted attack, and (iii) we get no discussion of what (if anything) experienced players can look to to help with their scripting.
In short: I've got nothing against examples of play, but they should (among other things) give well-explained examples of how to handle the tricky or important things, not just gloss over or ignore those things.