I said "crunch, not fluff" but what I really would have liked is "maybe crunch, but definitely not fluff".
Of course, I never took the Great Wheel as more than a guideline and Sigil was stillborn, IMO. I don't remember the Great Wheel in BECMI, but I do remember the spheres (Entropy, Energy, Thought, Matter, and ?Time). Likewise, I remember when the plane of Shadow was tied to each specific material plane, rather than tying together the multiverse -- which was the job of the astral.
Crunch-wise, BECMI had "elf" as a class, not a race. And clerics haven't always had 9th level spells -- or spells at 1st level. Illusionists used to be a separate class from magic-user/wizard. They also had their own spell list that overlapped the wizard, rather than being just a subset (in this way, 4e may end up being a throw-back, from the sound of things).
And I don't think having at-will spells for wizards (or a magic missile that can miss) is any more significant a change than the priestly spheres in 2e. For that matter, 1e clerics who followed a demigod couldn't get higher than 5th level spells (IIRC -- I know there was a restriction).
Powers for fighters is no bigger change than adding in feats and/or skills. Heck, if they'd dropped feats, it could be said that martial (and some other) powers grew out of feats the way skills grew out of non-weapon proficiencies. The big deal is that they are intentionally increasing symmetry in 4e (wizards have powers, fighters have powers, can we use a similar system to track them?).
And, there are some crunch-supported fluff that changed pretty dramatically. Demi-human level limits, "name level", and overall monster difficulty in 1e strongly indicated that anything above 10th level (and 5th level spells) were extremely unusual. The ranger went from a tough border guard with a chip on his shoulder to a ambidextrous skirmisher and archer with a religious tie to nature. Elves couldn't be raised or resurrected in 1e because they didn't have souls. And I'm still trying to figure out why 3e clerics channel positive/negative energy, rather than the power of their god.
Finally, there a few things that are non-changes in 4e, regardless of perception. Square-based measurements just replaced inch-based measurements. Neither is "more wargamey". Today's wargamers just prefer grids to tape measures.
So, no. I don't think fluff has changed more significantly. Quite the opposite -- it's always changed quite a bit both during and between editions.
Without the crunch in front of me, I can't say for sure. What I've heard, though, makes me think 4e is a significant change -- along the lines of BECMI vs. 1e or 2e vs. 3e, rather than 1e vs. 2e, Holmes vs. BECMI, or 3.0 vs. 3.5. But, I don't think it'll be significantly greater in scope of change than those.