Come on folks, settle down--don't forget, we RPGers are an aging group and nerdrants can be hazardous to your health!

Plus, we've got to stick together, especially if the industry really is dying; who else do we have?!
This thread was not meant to enter into the question of what is and is not D&D; that could be an interesting conversation (assuming those involved could behave) but it wasn't the intention of my OP to go there. Rather, I was posing a hypothesis and asking, if you don't agree with my hypothesis, what is your answer to the "hate of 4E"? All I've seen is that there are different reasons, that my hypothesis is wrong perhaps as a dominant or over-riding reason, but that it may be true for some, even many.
Of course despite the above paragraph, I wish to address the following:
As soon as we all start arguing about "what is D&D," we have to be very careful. For me, there is only one line if inquiry, that I know of, that might actually further the discussion. To date, I have yet to receive an answer. It is:
At what point, in your opinion, do the accumulated changes to a game actually produce a different game? In other words, what would have to happen to a hypothetical future edition of D&D to make it "not D&D anymore," despite having the brand name on the cover?
If you can't answer that question, then your definition of D&D is functionally meaningless. It would be like trying to do science with a non-falsifiable hypothesis.
But can anyone answer that question? And does that, therefore, mean that everyone's definition of D&D is functionally meaningless? Maybe so. But I would take it one step further: because no one has come up with an adequate definition of what D&D is, we cannot really say that 4E is
not D&D because of the continuity of themes, tropes, and rules that it
does share with the D&D lineage. In other words, it has enough D&Disms that the owner of the trademark felt they could brand it with the name "D&D," and those who enjoy playing it--and many besides--call it D&D. When it comes down to it, it is only a relatively small percentage of D&D players that would actually claim that it is "not real D&D," even among those that don't like it.
To put it another way, the onus is on those declaring that 4E is not "real D&D" to support their claim in order for it to hold water beyond their own subjective inclinations; it is not on those that see it as D&D because of the above mentioned elements and, of course, the nifty little brand name on every 4E product (this is not to say that WotC could brand a can of tuna with the D&D trademark and it would be "real D&D," but that if you add the two together--shared elements with previous iterations of the game and the trademark--you come up with, well, real D&D, just a different form of it than some are used to).
How many boards need Theseus replace on his ship before it isn't the one he started on? How many times has your body replaced every cell, rendering you a completely new being?
Essentially it's a matter of perception.
As long as every change is minor, incremental and everything looks the same, Theseus may well tell you that he's still on the same ship, despite having mo original parts.
You probably think you're still the same "you" from when you were born, but except for neurons in your cerebral cortex, the human body replaces every cell in your body about every 10 years. You may LOOK like "you" and think like "you," but really, your brain gets a new chariot every decade.
So where "new" comes into the equation regarding RPGs is a matter of entirely subjective perception. Changes that made 4Ed "not D&D" to me (to answer your question, 4Ed achieved that status for me) may not be enough to sway someone else from accepting it as the same game they've always loved...maybe better.
Yes, it is a matter of perception. But I think your post only further supports the notion that 4E
is D&D in a sense beyond any individual's viewpoint, that is as an inter-subjective agreement. You are still you, even though the parts that make up you are different than what they were 10 years ago; why? Because you are more than the sum of your parts, you are more than just any iteration of who you have been at any given time in your life. You are no less you as a 40-year old as you were you as a 4-year old. You are the entire process, the enter being-in-becoming.
Why isn't the same true of D&D? Well, it is.
The Theseus's ship analogy doesn't quite work because you use the phrase "the one he started on." As soon as
any changes are made, it isn't "the one he started on." By that definition, only OD&D is real D&D, and everything after--including the supplements--isn't "the one he started with." Therefore the definition and analogy is false.
"The one he started on," or in the case of D&D,
the edition we started with, is different for a lot of us. For me it was 1E (well, a first exposure with one of the early Basic sets but then on to AD&D; we're talking 1981 or 82). 4E isn't "the one I started on" but it is no more or less "D&D" than 1E was. Why? Again, because it is part of the same lineage. It is a development from OD&D to Basic and AD&D to BECMI and 2E to 3E to 3.5E to 4E to Essentials to 5E and beyond. It is all one lineage, one overarching "meta-game." Each very is different to varying degrees, but they are all D&D. One doesn't need to like a given variation to call it D&D, but one's dislike of a given variation is not grounds in and of itself to call it "not real D&D."