With a consistent platform, developers of Metro style features within Windows can now leverage the standards and platform to ensure their components are accessible. While the features are designed, developed, and tested, Microsoft continually tracks the progress made towards accessibility. When the build for the Windows 8 Developer Preview was released, the team had been working on accessibility. However, they still had bugs that impacted High Contrast, keyboard navigation, and programmatic data for the ATs to consume.
They are by no means done, and they continue to drive the accessibility requirements across the team to ensure they meet their goals. In each public release of Windows 8, you will see improvements being made in this area.