Adobe announced today that they're open sourcing the Flex SDK (which includes the compiler, debugger, and Flex ActionScript libraries). It shouldn't come as too big a surprise, considering the recent MPL release of their ActionScript 3 VM to the Mozilla Foundation, Tamarin.
The model, as with Postscript, and, quite frankly, Windows, is the "Platform Effect" - monetizing both the runtime (Postscript/Windows/Flash) and providing rich(er) enterprise level authoring tools and functions (Authoring tools, servers, etc.). Releasing the specifications and "core" tools creates the illusion of freedom in tool chain, while actually delivering vendor lock-in - which isn't necessarily a bad thing for developers if (a) there's runtime ubiquity, and (b) the developer's not on the hook for distribution costs.
And getting developer buy-in (lock-in?) creates a "virtuous cycle" of scale for the platform provider... ultimately why API and specification ownership is so critical in the technology business cycle.
Although I think Adobe's Apollo (which is Flex driven) is still slightly off in its execution of product distribution, overall the company is doing a good job driving a giant truck over the ongoing bungling that is WPF (I mean... Silverlight).
And (naturally) this will impact (squeeze out) smaller players like Laszlo, Haxe, and mtasc more than affect the big players...