I'm not trying to argue Role-playing vs Roll-playing, as either can be done in a fluff light campaign. I also understand that D&D started off as war-gaming, but I would like to point out that Gygax (and others), turned that war game into D&D by adding wizards and elves and such. Then he tweaked that game rules to better fit what happens when a wizards throws a fireball down a dungeon corridor as opposed to a siege engine attacking a castle wall. He essentially designed the rules around the fluff, not the other way around.
Which I think is what wrong with 4e. There were already alternate games with different rules that had various strengths and weaknesses. I admit I was not much of a fan of the rules-changes themselves, but after a year of trying and finally realizing I wasn't going to be able to play in the same worlds I loved playing and reading about as a kid, I just gave up.
As soon as the design team realized they would have to make up something like the the "spell-plague" to explain all the changes they were making in one of their worlds, they should have realized they were doing the wrong thing.
You keep talking about adding wizards and elves to the game like that was what added the fluff. It was a fantasy wargame, those are part of the genre. I will agree that perhaps Gygax designed the rules around the "fluff" in the sense that he designed the rules to mimic much of what he had read in fantasy, in particularly Sword and Sorcery, fiction but again it was the mechanics and being able to make up your own character within the rules of a systemic system that attracted people to DnD. That's the difference between DnD and Cowboys and Indians, DnD is essentially Cowboys and Indians but with rules present so you don't have the "I shot you your dead" "No, I'm not I ducked down in time to make you miss" arguments. Yes, those mechanics may have changed from being to determined by a DM to hit chart, to a THACO chart, to BAB or some such and the way your X type damage spell was described my have changed from all creatures in a 20 ft readious burst with a range of X amount of feet +10 ft/per level to area burst 3 within 20 squares but the overall point is the mechanics, the crunch of how building your character within the guidelines provided and with the various rules in mind is what is attractive (at least as equally as the fluff) to DnD...otherwise people would just play a fantasy version of cowboys and indians or some such. This is the reason why DnD as despite the various editions maintained being a class and level based system, because a class and level based system provides a clear and systemic way to measure the success of your character and creates a sense of accomplishment (no matter how illusory) that your character has achieved something mechanically and is getting mechanically stronger vs other games that say okay you used X skill this game so instead of a level you gain +1% point to X skill. The C&L system and heavy mechancis is what also made Pathfinder strong.
Secondly, the designers of 4th did write the rules with Fluff in mind. I will use FR specifically sense you mentioned the Spell Plague. The whole point of 4E from a world design perspective was "Points of Light". The heroes are brave beacons of hope in a time that is dark and perilous. FR, since mid-to-late 2E had gotten far away from this root. When FR first came out you had the Old Gray Box with the skeletal blood rider on the front pulling the woman's hair as they rode on horseback, the sky was covered with storm clouds in the background...FR was dark and gritty almost like the Word of Warhammer in tone but with more magic prevalent. Over the years it brightened up to the point as one designer put it FR was almsot like Keystone cops. It became ligher and more whimsical, you had the SEven Sisters, The magister, Khelben Black Staff Arunsun, Drizzt, and of course Elminster running around so no matter how "dark" things got in the world (like the Time of Troubles) it never really seemed that perilous or dark (not like the early Darkwalker on Moonshae novels) and 3.5 did nothing at all to change this. So, with 4E they needed something to tone done the lightness to talk Elminster and other NPCs more into the background and make the Realms more of a PoL game, hence the Spell plague was invented so the mechanics were made with the fluff in mind. So, is your problems with the mechanics of 4E or the fluff of 4E. If the problem is with both or you don't like one or the other that is fine, but to say this edition didn't do what other editiions did is in my opinion part of an ongoing issue of people romanticizing previous editions.
An example, of this would be earlier in this thread when someone mentioned how much more freedom you had in 2E and how 2E rules like THACO and such were not all that bad. I say this is a romanticization. I played 2E and still have the core books for that edition. I remember things like race/level limits in 2E. Humans were not allowed to multiclass. So, in 2E if I wanted to play a Fighter-Rogue like Conan (an iconic archetype of fantasy literature) as a human it was hard to do. You would have to dual class as a thief (although conan was a barbarian before he was a thief) up to a few levels and then dual class into Fighter (with the barbarian kit), but never ever be allowed to pick up rogue profiencies/ abilities anymore because the rules of dual classing stated once you switched into your new class you could never go back and pick up levels/abilities from the class you left Also most non-human races had level limits on how far they could progress in each class. If you used the optional rules presented in the 2E DMG it allowed certains races to progress a little further, but they were stilll caped. For example, (and I am just going from memory here as I don't feel like digging out my 2E DMG) Half Elf was the only 2E demihuman race, as they were then called, that was allowed under the expanded advancement rules to be unlimited in class advancement as they had unlimited advancement in the Bard class, but every other race maxed out around 12th level I believe. Clearly, these were not well designed rules.