First, I think, it's necessary to point out that the assumption that Microsoft would continue to build market-share in the generation after the Xbox 360 was based on nothing but wishful thinking. I can't tell you how many times over the last few years I've seen people post that the next Xbox would "win".
The truth, however, was that the PS3 had a much higher sales rate than the 360. On a monthly basis, it consistently outsold the 360. Throw out the Kinect anomaly and the numbers get even more skewed. Simply put, the Playstation brand has been the better selling brand through most of its lifetime. Microsoft did a wonderful job; they killed off the original Xbox in order to launch the 360 with a year's head start, they poured vast amounts of money into securing games and into marketing, they created an excellent online experience, and they secured Halo and Gears.
But assuming that the next Xbox would dominate? That's kind of unfair to Microsoft. Playstation was the stronger brand this past generation even with all the mistakes Sony made early on. If both companies had continued the way they left off, there really was no reason to assume that Microsoft had the console war in the bag.
So, in that regard, I don't see how Microsoft can be blamed simply because Sony got their affairs in order.
As for why Playstation has been the stronger brand, most of that goes down to World Wide Studios. It has a more diverse catalog of games, which gives it more appeal in more places. Outside a few exceptions, the 360 has had to depend on third-party titles in most genres. To Microsoft's credit, they've seemingly realized this, as they've kicked up internal development by a massive degree.
