Every gen is different though. Last time PS2 was sitting on 150 million and Xbox on 25 million. MS had a mountain to climb to catch up to parity, which Sony's missteps allowed them to do. This time, they go into the gen as roughly equals.
IMO - that is the problem. They are not. They are launching side by side, first trying at a higher price with an expensive add-on that is/was central to their vision but at the cost of performance - then later this year, at price parity, without a one distinguishing feature they had but still at a fairly big performance differential. At the same time. Effectively, we now get Xbox brandname vs. the PlayStation brandname (+ better performance).
If Microsoft had come out at the same time, at the same price with equal machinery and a "vision" that target the core-gamers (+ perhaps the Kinect stuff) at the same price, but only slightly higher - it could have worked. I would think it would be logical to assume that most 60-80million Xbox users outthere would be happy to upgrade and stay on the platform they've been happy with to beginn with.
The high price, the muddled vision of chasing after a more livingroom centered device with Kinect in its main focus scared away a lot of its loyal gamers. As the poll created I think showed at some point - there were (at least on this forum) more Xbox users willing to switch to the PlayStation brand than the other way around. I also think that many of the Xbox most loyal fanbase - the fans and consumers who made the original Xbox a moderate success - come from a PC gaming background. The Xbox was the one platform that catered more so to those gamers - offering better graphics (than the PS2), easier development (bringing along lots of PC centric developers) and as a result, got a lot of shooters which is a very attractive genre on PCs. They were also the first to offer a dedicated online service (Live) which layed the ground work for the future with online-gaming on consoles.
I see these fans of the original Xbox console to not be catered for with the Xbox One. X360 continued the trend the original Xbox started (good online gaming, good gaming performance, perfect price point, all a year ahead of the opposition), but the new Xbox One did not. There are no doubt still a lot of loyal fans of the Xbox brandname, but even if a third of the other fans were willing to change ship - either going back to PC gaming or to the PlayStation brand (because that's the brand that effectively is offering the best performance at the lowest price), it doesn't paint a pretty picture for the future IMO.
The PlayStation brandname is strong. For years, it stands for diverse gaming, from family games to strong Japanese support. Over the years and since PS3, it also caught up on multi player gaming (at the time for free), a strong online service and it also has most high selling shooters through multi-platform support.
The bad news for Xbox is that the PS4 is perfectly priced, focused on what core gamers want, has a lot of performance for its price - and best of all - is easy (if not arguably easier) to develop for than the Xbox One - something it failed to do on both the PS3 and PS2. This means that many multi-platform developers can easily extract more performance from the PS4 because both machines are quite similar with the exception of the easier memory subsystem and more performance. This results in that the majority of multi-platform games will likely look better on the PS4 - ranging from hardly distinguishable to noticable.
What's keeping the Xbox One in this race so far is because there are quite a lot of happy X360 customers outthere, that don't mind the performance differential (or don't think it's big enough) and because lots of friends are willing to stay on Xbox - so staying with the brand means you still get to play with your friends. Then there are the few Xbox centric exclusives. Still, I personally think - they either need to lower the price further, or keep Kinect as a distinguishing feature. They've killed of the latter and sadly, there's nothing they can do to get back that performance differential.
At the end of all of this; I do wonder sometimes if the Xbox gamer (the core-gamer) - the one who effectively made the original Xbox a success - is more interested in graphics than perhaps the loyal PlayStation users outthere. Could this be a factor?