On the contrary to what you might think, Flash and Flex can be fully accessible.
Since Version 6.0 of Flash Player in 2006, Macromedia has thought about accessibility by implementing a screen reader that is compatible with Microsoft Active Accessibility to support playbacks of flash websites.
In 2009, Adobe released version 9.0, the first player to allow rich media to be accessible to people with disabilities. In doing so, they tried to perfect their support for people with any disability (visually impaired, mobility impaired, hearing impaired etc.) and provided numerous accessibility specific components and a guide of best practice.
In the past year, the Adobe team has worked hard with Freedom Scientific in order to make Flex fully compatible with their famous reading software, JAWS. They have also worked with The Paciello Group and SSB BART Group (two consulting companies specializing on web accessibility) to ensure that the new Flex 4 will provide accessible standard controls. Today, the new Flash Builder contains a large selection of accessible components to provide support for users with disabilities.
Making Flash and Flex accessible has not been about a matter of technology, but of wise preliminary planning. Accessibility needs to be a developer's concern during the early stages of a project, and should be focused on throughout the whole development process rather than postponing it until the end. If youre interested in finding out more about Adobe and Accessibility, their blog follows their efforts to making rich media more accessible to all.