The changes from 3.0 to 3.5 largely overwrote the works of 3.0, such that those playing 3.5 no longer used the 3.0 core books or splat books.
D&D Essentials will not do this. And none of the existing 'updates' to the game have rendered unusable any of the prior material. There have been individual powers and class elements that have changed, but the character - both before and after any rebuilds - remained a 4E character, and drew from the same pool of resources and options. And the vast majority of the updates have not resulted in sweeping rebuilds except for a very small handful of cases... or by those who were after very specific power combinations and felt the need to rebuild when those gamebreaking elements were fixed.
Sounds like you're using the conclusion to argue the premise. A 4e barbarian who has experienced revisions to many of his powers, feats, and magic items--making some illegal and others ineffective--is still a 4e character, but somehow a 3e barbarian who finds the some of his class features changed in 3.5 is a diiffernt character completely? If there's a thrust to that argument, I must confess, I'm missing it. Some 3.5 characters have had to be rebuilt, and some 4e characters have had to be rebuilt. Same deal.
As to saying 3.5 overwrote 3e books, but 4e revisions don't overwrite 4e books, not sure how you could say that either. 4e updates frequently say "replace sentence X and paragraph Y with this text". That's about as overwritey as it gets.
If you want to play 3.0 characters in a 3.5 adventure using monsters from a 3.5 book, that's only going to be an issue in a small handful of cases--an amount which you're willing to allow for with 4e updates. Conversely, many update-aware 4e players have indeed come to the conclusion that they can't trust what they look up in print. I know nobody in my group trusts the PHB to build a character. CB or bust.
And it's not just character info that's changed. The PHB no longer contains for stuff like skills, conditions, effects, combat. If there's a question about charging, are you better off looking in your PHB, or your rules compendium?