It's important to note that these worldwide sales trends can look very different when you zoom in on individual regions. In Japan, for instance, the Wii U is actually winning the lifetime sales battle, according to tracking firm Media Create, riding its earlier launch to over 2.2 million aggregate unit sales (though the PS4 is leading in sales for 2015 thus far). The PS4 has sold over 1.4 million units overall in Japan, while the Xbox One is limping along with a paltry 50,000 units sold in the country.
Excluding Japan, the Xbox One looks slightly more competitive, and the Wii U looks slightly less competitive. Subtract these numbers out from the worldwide picture and the market in the non-Japanese-speaking world starts to look slightly different, though perhaps not materially so. We've also seen some reports that the PS4 and Xbox One are running much closer to sales parity in North America than they are in the rest of the world, though the source for that information isn't secure enough for us to share those specific numbers confidently.