Posters like Opiate make a good point in that the worry isn't so much the PS4, but rather the health of the second and third consoles this gen. Wii U has done awfully, and Xbox One did pretty well at launch, but then had its sales collapse recently which is certainly worrisome.
Nintendo's approach is surprising to me. In many ways, they are just letting the console die right before our eyes, unlike their aggressive attempts at salvaging the 3DS early. Wii U certainly has a great lineup by now, but the lack of a genuine price drop is puzzling me. Especially with Mario Kart 8 out now, I would have imagined that hitting a $199 price point would really go a long ways towards improving their situation. Perhaps they are simply unwilling to take a loss, and feel like any attempts to do so wouldn't yield enough improved software sales over time to offset this investment. It feels like they've given up and have taken the completely opposite approach that Microsoft has -- they are not getting rid of the GamePad and dropping the price. It will be very interesting to see how these different strategies pan out. I'm inclined to believe Microsoft is making the right move by acting swiftly to decrease costs for a peripheral that consumers don't recognize as value-added.
Still, another good point is that simply analyzing hardware sales and comparing the generations may not be the best approach. There were a lot of multiconsole owners last generation, so profit and software sales are more important metrics, in my view. And right now, at least for new IPs like Watch Dogs, software sales on the new generation are quite healthy. I believe publishers are better prepared for managing costs of projects and knowing when one needs to be cancelled rather than throwing good money after bad games.
Microsoft's biggest challenge is to get people to buy multiple consoles. The 360 came out early, was substantially cheaper, had a superior online infrastructure, and was comparable in terms of power, even though many 360 owners were previous playstation owners. This led to the 360 being a primary console, and Sony struggled to regain their userbase. Throughout many years of excellent titles and exclusives, along with Blu-ray affirming itself as the only media format, they were able to get back in the game, and I'd argue a lot of their audience also owned another console, primarily a 360.
With this gen, Microsoft doesn't have these advantages, and Sony built up goodwill with their consumers over the course of many years which now allows the PS4 to enjoy the primary console status...Microsoft can't change that, but they can get PS4 owners to buy Xbox One's. More Halo, Forza, Fable, and Gears simply aren't going to cut it. Microsoft needs to establish more differentiating AAA projects that take creative risks, and in the absence of Bungie, they need a premier studio that surprises and tends to be rock-solid on quality like Naughty Dog. So far Phil Harrison hasn't given me any reason to believe that the Xbox One will be able to convince as many folks to buy another console as the PS3 did, and I feel it's quite unrealistic for them to expect much more than 40-50 million units sold this generation worldwide.