An advantage of Flash is also the products from Adobe.
Adobe Flash (or Adobe Flex) offer quite a lot of functionality to easily develop games and applications.
When using DirectX or OpenGL, apart from the fact that such Apps can't be run in the browser, you still
have to develop your own engine and tools. That slows down considerably.
On the other hand I also don't really like Flash applications because the usability is quite
low in most cases (no usable full screen possibilities, using right click is limited, ...).
@the.weavster
There is also 'Adobe Flex' that offers many classes and controls for application development.
It's built into the Eclipse editor and even offers a GUI designer.
Greetings,
Shield