I think the term is an appropriate reaction to the cutting/consolidation of features that have no clear reason to be cut or consolidated, other than to appeal to the widespread gaming community who may not "have" the patience/intellegence to master these features, in the eyes of the Exes.
Example: FO3 to FO:NV- cutting of Big Guns and putting in Survival isn't "dumbing down." Heavy Weapons was a catch-all for various weapons that were not rifle or pistol-like in nature, despite having skills for various types of weapon damage. And Survival added a new feature, basically cooking, to the game that wasn't there beforehand, which enchanced the roleplay aspects of the game.
However, in Morrowind there was at least 5 melee weapon types. In Oblivion, this was cut down to two, removing one branch (Spears) and consoldating four skills into two (Blade and Blunt, previously Long blades, Short blades, Blunt, and Axes.) Furthermore, Skyrim switchess this to One-handed and two-handed weaponry. There is no clear reason for this consolidation, and there can be no explanation as to why someone who is profiecient with a dagger is equally proficient with an Axe or a longsword- unlike with our heavy weapons example above, these skills were previously clearly defined and made sense in terms of damage type, and the "new" skilltypes do not bring much to the game. In this case, the term "Dumbing Down" is appropriate- we can only reason that the exes made the decision to "simplfy" skills to appeal to the masses, rather than the reason of "this skill doesn't make sense, logically speaking. Why are we using it?"
Except that what you fail to take into consideration is that the two overarching weapon types (one-handed, two-handed) also have specializations within them, so there are specializations in blades, blunt weapons, and axes, both with one and 2 handed versions of it, as well as specializations in daggers, and specializations in dual wielding. So Skyrim offers your blades, blunts, axes, daggers, and dual wielding, which is 5 melee combat types.
And putting perks into blade, axe, blunt, or dagger specialization is no "simpler" or "less complex" than selecting short blade, long blade, blunt, or axe as a major skill.
The things that were removed for Skyrim also had things to replace them.
-Armorer was removed, replaced with a more in depth and complex crafting system with Smithing
-Mysticism was not removed, but rather merged with Alteration and Conjuration
-Hand to Hand was removed as a skill, but is still in the game to use, including perks to further specialize in it
-Unarmored is still not in the game as a skill, but there are perks included in the game to allow specialization in it, which is a step up from Oblivion
-Athletics and Acrobatics were removed in Skyrim, but more fleshed out skills like Pickpocket and Enchanting saw their return to the series.
-While there are only 18 skills in Skyrim as opposed to 21 in Oblivion, each skill has multiple fields of specialization that allow for deeper character customization than Oblivion or Morrowind did. I.E.: Master Conjurers can be Necromancy specialists, Atronach Conjurer specialists, Bound Weapon specialists, Master Destruction mages can specialize in specific elements, One-Handed fighters can specialize in blade, blunt, axe, or dual wielding, and so on and so forth.
-Spellmaking was removed, but the casting gameplay mechanics were enhanced to allow for new spell casting types that weren't possible in previous games, and the ability to equip multiple spells to mix and match effects.
-Attributes were removed, but perks allow for all of the same in game effects as Attributes did (the only thing missing is speed)
-Dungeons and quests now have puzzles to solve, and there is an element of choice that hasn't been there previously
^ And that essentially is my problem with the entire "dumbed down" argument - people who use that term are throwing it around because they don't prefer the newer methods, but they fail to realize that things haven't gotten simpler than before. If anything, they got more complex. They simply look at 18 skills vs. 21 skill (or 28) and fail to examine that skills have gotten more in depth. They simply look at the fact that Attributes are gone, and fail to see that all the same effects that Attributes provided in previous games are still there in perks. They may not prefer the newer methods, and that's cool, but to toss around the term "dumbed down" is incredibly insulting.
It's even more insulting when I've been a massive fan of Morrowind since it's release 10 years ago, and the claims being made about Morrowind and just how "intelligent" it is are flat out false. Morrowind had map markers, they just didn't have on screen quest markers. Instead, you had to keep opening your journal and map to get your bearings. It accomplished the exact same end goal, one method just removes the tedium of constantly going into your menus. Dialogue was no more complex or in depth with text than it is with spoken dialogue. NPC's constantly had the same rehashed dialogue as every other NPC in the town, and unique quest dialogue is no more in depth than Skyrim's. Skyrim has plenty of in depth quest dialogue and directions and instructions, people just don't realize it because it's not jotted down into a journal. But there was plenty of "let me mark that on your map" quests for you in Morrowind that gave you bright yellow blocks on your map telling you where to go.
I really don't care if you prefer Morrowind's methods of doing things or Skyrim's. Frankly, I don't care if you absolutely despise Skyrim and think it's the worst thing ever or not. But the term "dumbed down" is an incredibly rude, and insulting way of going about expressing your displeasure, because it's not only negative towards the game, but it's negative towards the people who like it as well. Using terms like "dumbed down" is not constructive criticism, it's relying on emotional sensationalism to express your point. If you can't express your point without using rude and insulting terms, then you don't deserve to have your opinion taken seriously, and I will lend it no validity. As far as I'm concerned, people who use the term "dumbed down", or similar terms, are no better than common forum trolls. Express your point in less insulting terms, and I will be more than happy to listen to your complaints.