See below for a small capture of Microsoft’s evolution of the 3 screen approach, PC, Mobile and TV.
The 4th and most recent article below is clearly the most interesting today, but the progression itself is also interesting.
They are also positioning the surface tablet device shipping Friday as a PC because it has a detachable keyboard. In that way, they are saying the PC is still relevant, it’s just gone to a new form factor, but they still give great value to the TV (XBox) and Mobile (Windows Phone 8)
Why Carriers and Microsoft Need Each Other June 27, 2008
PC Is Just One of ‘Three Screens,’ Ballmer Says By James Niccolai, Jan 7, 2009
Microsoft’s 3 Screens and a Cloud – in a single image August 16, 2010
Microsoft announces new Xbox SmartGlass experiences and commences free streaming Xbox Music Posted on Tue, 23 Oct 2012