WinFX SDK vs. Indigo/Avalon Redist
You've probably seen the pre-release of Avalong and Indigo Beta 1 RC, and if you downloaded the content from https://www.microsoft.com/downloads/details.aspx?FamilyID=b789bc8d-4f25-4823-b6aa-c5edf432d0c1&displaylang=en&Hash=338QXSB, then you've likely downloaded the redistributable instead of the entire WinFX SDK.
While you can develop against the redistributable, you don't get the documentation, samples, etc. For those little pieces, you need the bundle of joy that is the WinFX SDK which is hiding behind a the little innocous link on the page within the statement, "There is also an updated WinFX SDK, including documentation, samples and tools available for this release."
If you're like me, you never read that far on the page the first, second, third and even fourth times you visited the page and may have overlooked it. Rumor has it the documentation contained with the WinFX SDK is more up-to-date than the documentation on msdn.microsoft.com.