Apple does this, I believe, because they don't want their customers to be either dismayed with the realities of the updates nor confused by them. Too much information, like the world of Linux, can cause the customer to feel overwhelmed. Buying and owning a Macintosh should be a happy experience.
Unfortunately, that's a fantasy world. Even the most Pollyanna Apple customer is confronted with a vast array of technologies to integrate. There are dedicated backup devices, other external drives, printers, iPhones and iPods and who knows what else that all have to be kept working in unison, perfectly.
Worse, it looks unprofessional and it makes Apple look like it has something to hide. While security updates are detailed fairly well as to the documented vulnerabilities that have been patched, other updates, like the recent Apple TV 2.0.1 update appear with no explanation at all. At iLounge on Monday it was reported that some users were having issues with the update. There's nothing more frustrating than applying an update, because Apple puts it out there, and then having problems that must be solved by asking others in the forums, "What the hell just happened?"
Corporate users hardly ever install updates until they understand the impact on their systems -- the ones they try so hard to maintain in a delicate balance of usability and stability. That's why Red Hat and Fedora Linux branched. Red Hat remains stable and supported for the enterprise. Fedora is free to experiment. Constant tinkering and fine tuning leads to unstable systems.
It takes some time to understand what a problem is, then create a solution and test it. As a result, Apple engineers know what the problems was, why they fixed it and how. Hiding that information from the paying customer for the sake of the illusion of carefree simplicity is out of sync with the needs of customers.
Today, it was announced that Apple is being sued for allegedly making false claims about their 2nd generation iMac 20-inch screens. This is another trust related issue. One of the keys to making a no-brainer decision for Apple is that the customer trusts what Apple is doing in all areas, design, hardware, user interface and security. Backing away from full disclosure may make Apple look like a happy-go-lucky company, but it also strains our trust.
Right now, today, we need trust a lot more.