You’ve described only symptoms in Windows Is So Slow, but Why?, not the underlying problem. Closed-source software development has a scaling limit, a maximum complexity above which it collapses under its own weight.
Microsoft hit this wall six years ago, arguably longer; it’s why they’ve had to cancel several strategic projects in favor of superficial patches on the same old codebase. But it’s not a Microsoft-specific problem, just one that’s hitting them the worst because they’re the largest closed-source developer in existence. Management changes won’t address it any more than reshuffling the deck chairs could have kept the Titanic from sinking.
Apple has been able to ship four new versions in the last five years because its OS core is open-source code. Linux, entirely open-source, has bucketed along even faster. Open source evades the scaling limit by decentralizing development, replacing top-heavy monoliths with loosely-coupled peer networks at both the level of the code itself and the organizations that produce it.
You finger backward compatibility as a millstone around Microsoft’s neck, but experience with Linux and other open-source operating systems suggests this is not the real problem. Over the same six-year period Linux has maintained backwards binary compatibility as good as (arguably better than) that of Windows without bloating.
Microsoft’s problems cannot be fixed — indeed, they are doomed to get progressively worse — as long as they’re stuck to a development model premised on centralization, hierarchical control, and secrecy. Open-source operating systems will continue to gain at their expense for many of the same reasons free markets outcompeted centrally-planned economies.
The interesting question is whether we will ever see a Microsoft equivalent of glasnost and perestroika.