Some speculations about Microsoft internals and fights against Dev Div and Windows Div about UI framework. Speculations that can be not far from the truth.
Understanding the Windows 8 Jupiter fiasco | Brill Skills.
EDIT: More informations on same subject: Windows 8 for software developers: the Longhorn dream reborn? and
Premature cries of Silverlight / WPF skill loss. Windows 8 supports all programming models.