A walled garden is difficult and expensive to maintain. In Apple's case, it also requires a constant battle against the public interest, because they've carved out various niches in domains that intrude on interoperability, consumer rights, privacy, censorship, surveillance, tax evasion, child slavery, and so on. If they cede ground, they lose money, so they develop and execute strategies that minimize or mitigate loss in conjunction with maximizing gain.

Apple has no principles or ethics or morals to which it is bound; it's governed by an optimization algorithm that pits the profit incentive against the constraints of resources, legislation, and their public image.

Apple's only as effective as the humans who execute their assigned roles within the overall algorithm, so the organization is subject to the usual human weaknesses and foibles.

Pride. Arrogance. Bullheadedness. Complacency.

If these weaknesses infect the culture, spreading across many roles, then many things can degrade and spin out of control. Apple is just as mortal and vulnerable as MySpace, Yahoo, Sears, Blockbuster, or any other big company or institution.

Without the advantages afforded by the unsavory, unethical, and unprincipled aspects of their business, Apple might not be able to maintain their walled garden effectively. Apple's particular variety of golden goose may not continue to be compatible with the markets in which it currently dominates, since much of the regulation, litigation, and legislation will focus on Apple's effects on the world.

Lots of things could happen outside their control that would kill the golden goose. Lots more things could happen if they fall prey to human failure modes.