They're looking beyond the video game console. MS believes what happened with the smart phone will happen in the living room. There will be a convergence of all devices into a single device. XB1 is the stepping stone to the next set top box.
On one hand, you can think like this:
After Apple launched the iphone, google created the android, and many other companies copied after. Currently, smartphones are everywhere, and the old phone is mostly dead. If XB1 is the stepping stone, other box manufacturers will attempt to create the same type of thing, and gaming boxes will change forever.
On the other hand, you can think like this:
XB1 has a decent idea in creating an all in one box, but there's no way that all other box makers will stick a gaming machine in their product to compete(the exception being social games). My FIOS box can play some games, but they're not putting hardcore titles on it, and the same with the cable box I had before it.
I would like to point out that initially, Sony did try to market the PS3 as a media box that played some great games(bluray player that plays games). That initially went over like a lead balloon due to the price. As time went on, when bluray beat out HDDVD, more people decided that it's a gaming machine with a pretty good bluray player in it.
Sony also tried a shared computing concept first. The PS3 promise was that the box, when connected to the net, could find other PS3 consoles, and borrow processing power as needed from consoles which were not using all of the power of the cell. Ultimately, this was used most for the Folding at Home project, and nothing else.
What MS is doing now is just an evolution of some of these concepts IMO.