I think the lesson here is that what gamers really want are flavorful mechanics. Splitting them out into separate sections is a mistake; the two should be integrated, so that you take in the flavor at the same time you're learning the mechanic.
I tend to disagree with that; or, at least, I really appreciate that in 4e, there is almost never any ambiguity between what is "fluff" and what isn't. Nothing aggravated me in 3/3.5e like prestige classes/feats/whatever with pre-requisites which had no connection to mechanics (culture, organisation, race in many cases*, and even the odd case of gender).
Alignment was always the worst offender. Yes, okay, maybe you
designed that class to represent a berserking half-orc warrior, but it's perfectly for my concept for a mild-mannered poet possessed by a demonic spirit that occasionally seizes control. Sure, he isn't chaotic, and he's an elf not a half-orc, but were those requirements
ever designed to control power levels, or were they just put there because that was your concept? Granted, many GMs would agree, and allow a houserule, but in examples like those not everbody agrees on where the line between crunch and fluff lies. That, in my opinion, is when fluff is getting in the way of creativity, not stimulating it.
Anyway - including quality fluff with the mechanics is
excellent, and I'd never say that books should be pure crunch (even power names are flavour elements, after all). But I do think they should be always distinguished from each other, so that individual groups/players can fluff the mechanics differently if they choose. I think 4e does an excellent job of this; the mechanics have solid falvour attached, but they are clearly delineated and nobody needs to argue over whether or not "Str vs. AC" is a thematic restriction.
(*Race was sometimes a genuine mechanical concern, yes, but more often it was just a flavour concern.)