I could call out a few comments here, but I just do not see this one in particular.
How does 4E make your books of whatever edition useless? Did they spontaneously combust? Are they rancid now that the use-by date has passed?
While I see this as basically correct, there is a grain of truth to this.
The big difference between 4e and the 1-3e is that most maintained a level of backwards compatibility. 2e, at least the core (I'm not talking about Players Option stuff) was pretty much a streamlining of the 1e ruleset. I would say the ruleset is about 95% compatible with 1e.
While 3e introduced changes, they still kept what I would call a recognizable baseline. Rules such as saving throws were changed, more definitions were introduced, and etc, and there are new innovations like feats, skills, and rules for things like poison. But your core expectations are intact. There is still a wizard that has fireball as a third level spell, most of the spells are the same as they were in 3e, Gnomes are what we expected in the game system, the cosmology of the outer planes is similar to what started in 1e, and while magic items were streamlined, you still had your familiar Staffs, wands, rods, rings, etc, and they worked as similar as possible to 1/2e rules. (Maybe a few staffs or wands became rods). I would say you have maybe a 75%-80% compatibility if you wanted to adapt old supplements.
Whatever the motivations of the 4e team, we don't have what I call a very similar or compatible game system. It really fails the "familiar" test. Now everybody has powers, you only have at most half a dozen powers, abilities that have nothing to do with combat have been moved to rituals, the combat system is very tactical, magic items have changed, and the first release didn't preserve even all the iconic classes and races. Many things like monster lore and planar cosmology have changed as well. I'd say in terms of compatibility with older games of the line we are talking maybe 50% or less.
Simply put, if I played AD&D in the 80s, then was away for 10 years and wanted to start a new game, I can see a gamer more easily recognizing and enjoying the 3e game system. I can't see it with the 4e system. At minimum, even if they like the game, there's a big learning curve that's going to be involved, much larger than the 1/2 to 3e curve.
So yes, I see the point that the 4e books do invalidate older supplements. While this might have happened with 2e to 3e as well, it's probably a LOT easier to convert older modules from 1/2 to 3 than from 1/2/3 to 4. My 15th level Mage or 12th level paladin can go from 2e to 3e and still be very familiar. A 1e module can be converted to 3e and while it may be a little work it's still going to be familiar. When I played ToEE on the PC, it felt as close as you could get to the old 1e adventure with the new ruleset.
If you've invested a lot of time into 3e, especially considering the huge third party market, I can see 4e being a turnoff.
In the business world, there's a thing called "change management". It's what a company does when making changes - it manages them, because people often don't like them. It makes efforts to control customer expectations and views about the change.
Interestingly enough, I saw this mentioned in the 40 years of GenCon book, when they talk about 3e. Change management was undertaken by WoTC as well. I think the key differences were the following. First of all, WoTC as run by Peter and Ryan seemed to want to keep the D&D identity strong while also making the game a little more progressive--and they were actively seeking both old fans and new, especially fans who became disillusioned with the game. They reached out to creative types long ignored by the company. And the marketplace was a little different--D&D had just missed the bullet and TSR might have disintergrated, taking the game with it. I'm not really sure there was as much pent-up demand for a new edition of D&D this time around.
And I remember the playtesting and excitement building being a little more open and less secret. I was a playtester, and while I was under an NDA I was able to discuss some things without making WoTC paranoid--heck, this whole site started as a 3e news blog. But they seemed different this time around. If I remember correctly, a while back Andy Collins had asked playtesters who had criticisms to not speak to the public about them. It was also harder to get any news about mechanics.
I think only time will tell if the change management of WoTC with 4e was good or bad. Maybe after years have passed, this will either be a case study for success or failure.