I think the most significant part of this announcement is how they are dogfooding, Office for 'metro' and for the windows phone are using this Universal targeting.
They've been dogfooding for decades, that's a very core part of the developer culture at MS. (You can say many bad things about them, but they really do dogfooding all the time.)
Kind of... Still, they didn't use .NET, Windows Forms, WPF and countless data access layers in their core products (Office and Windows), which probably contributed to the fact most of these frameworks got obsoleted every few years.