1. Adobe isn't completely innocent. They're pretty close to a monopoly on their type of software and charge dearly for it (their Creative Suite costs as much as a MacBook Pro). They've done a lot to make sure there are no non-Adobe Flash players even when that's just hurting customers and not costing them money since they don't sell the player. They're not exactly "open" and "free".
2. Apple could be said to have an interest in not supporting intermediaries. Intermediaries are likely to create less efficient code and I'm sure they don't want to deal with developers using up their support time over things that are the fault of Adobe's Flash SDK or Novell's C# one.
3. It's also in Apple's interest to get people using Objective-C and their toolkit. It brings developers to the Mac by forcing them to buy one. That will have positive externalities in more software for the Mac. It gets developers into the Obj-C camp which means more people with Mac development skills. It means that apps can't be re-compiled for iPhone, Android, and webOS - and that's huge for customer lock-in. We all know how users get attached to their apps and I think it's easy to imagine Adobe building an Android compiler right after the iPhone one got finished.
Do I like Apple's stance? No. As a user and a developer, it's bad for me. However, Apple's the market leader and getting people to use their API gives them control and means that app developers will always be ready to use the latest new features they add while building a wall of incompatibility against Android and webOS that will keep users buying iPhones for apps in the way that users bought Windows computers for their apps for ages.
Jobs wanted web apps. Developers balked. Web apps would have been cross-platform (at least with Android and webOS). Apple responded to developers and now they've seen their chance to lock users and developers to their system.
Adobe isn't known for being open. Given the chance, Adobe seems to wall itself off as much as Apple. Companies tend to go for openness insofar as it's in their interests.