Ehhhhh, I think that it is still possible for Microsoft to make a comeback, to an extent; but the longer this goes on, and the wider the gap gets for Sony, the more energy and money Microsoft is going to have to burn to try and make up for the lost ground. Someone mentioned earlier in the thread that sales momentum is hard to counter, and the early lead the PS4 does translate into extra sales momentum; the gap isn't insurmountable (not yet, anyway,) but it isn't something that's going to 'Fix Itself When Halo Comes Out.' Getting back the U.S., for Microsoft, is likely going to involve some heavy discounts and very cheap bundles, perhaps more Titanfall-esque 'free game bundles,' and lots of other very expensive pro-consumer incentives.
That being said, I have noticed that even those confident that the Xbox will regain the U,S, don't really seem to hold such expectation for a global win, which makes sense. Even if Microsoft DOES regain the lead in the U.S., they likely won't enjoy the same dominance that the Xbox360 had over the PS3; with no reasons to believe that Europe is going to be any less of a 'Go Sony' territory than last time, Sony will likely maintain the global lead for the rest of the generation. (Barring some out-of-left-field success of the Wii U. o.O )
Zanten, Doer Of The Things
Unless He Forgets In Which Case Zanten, Forgetter Of The Things
Or He Procrascinates, In Which Case Zanten, Doer Of The Things Later
Or It Involves Moving Furniture, in Which Case Zanten, F*** You.
