According to this post on the Building Windows 8 blog, Windows Media Center will be an extra-cost option and DVD playback support is being removed from Windows 8 Media Player.

In the process of building a robust platform, we've also evaluated which in-box media playback experiences we want to provide. The media landscape has changed quite significantly since the release of Windows 7. Our telemetry data and user research shows us that the vast majority of video consumption on the PC and other mobile devices is coming from online sources such as YouTube, Hulu, Netflix, or any of the other myriad of online and downloadable video services available. In fact, consumption of movies online in the United States will surpass physical video in 2012, according to this recent IHS Screen Digest research.

On the PC, these online sources are growing much faster than DVD & broadcast TV consumption, which are in sharp decline (no matter how you measure—unique users, minutes, percentage of sources, etc.). Globally, DVD sales have declined significantly year over year and Blu-ray on PCs is losing momentum as well. Watching broadcast TV on PCs, while incredibly important for some of you, has also declined steadily. These traditional media playback scenarios, optical media and broadcast TV, require a specialized set of decoders (and hardware) that cost a significant amount in royalties. With these decoders built into most Windows 7 editions, the industry has faced those costs broadly, regardless of whether or not a given device includes an optical drive or TV tuner.

Our partners have shared clear concerns over the costs associated with codec licensing for traditional media playback, especially as Windows 8 enables an unprecedented variety of form factors. Windows has addressed these concerns in the past by limiting availability of these experiences to specialized “media” or "premium" editions. At the same time, we also heard clear feedback from customers and partners that led to our much simplified Windows 8 editions lineup.

Given the changing landscape, the cost of decoder licensing, and the importance of a straight forward edition plan, we've decided to make Windows Media Center available to Windows 8 customers via the Add Features to Windows 8 control panel (formerly known as Windows Anytime Upgrade). This ensures that customers who are interested in Media Center have a convenient way to get it. Windows Media Player will continue to be available in all editions, but without DVD playback support. For optical discs playback on new Windows 8 devices, we are going to rely on the many quality solutions on the market, which provide great experiences for both DVD and Blu-ray.