Internet Explorer 10 will Ship with Adobe Flash
Two years ago, Microsoft declared that the future of video on the web would be powered by HTML 5. Today, however, a lot of web video content is still delivered via Adobe Flash technology. So, in a somewhat surprising move, Microsoft is integrating Flash directly into Internet Explorer 10 on Windows 8 and doing so in a way that does not undermine the safety and reliability of the Metro environment.
... Adobe actually provided Microsoft with source code access to Flash, allowing them to seamlessly integrate the technology into IE 10. Thus, Microsoft did not need to make an exception to its no-add-on policy for Internet Explorer Metro. By making Flash a part of IE 10, it can ensure the code meets its own standards for reliability, compatibility, security, and, probably most important, performance.
Remember, Hachamovitch noted that Flash was an important part of delivering a good consumer experience on today’s web. So, Microsoft has extended the Internet Explorer Compatibility View list to include rules for popular Flash-based web sites that are known to meet certain criteria. That is, Flash is supported for only those popular but legacy web sites that need it. This feature is not broadly available for all sites.
This move, while initially surprising, is entirely in keeping with Microsoft’s long-standing commitments to backwards compatibility. (Source