Well, regardless of anything else, they don't need to re-publish the core rules with every update they could have made. Just re-publish them once every 7-10 years, somewhere between 3.5 and 4.0, y'know, when they have substantial changes. They could even release it as "PHB II" or "The Next Edition," with a host of new options, saying "Your old stuff still works, and now here's some new stuff using a slightly more cohesive ruleset, add these into your campaign as you go, we will use them going forward."
This would have a similar effect to a new edition without the complete disconnect from the previous edition. A "sweet spot" between 3.5's minor changes and 4e's major changes.
That's a false requirement (regardless of anything else).