It looks like the Internet of Things could be the next big computing battleground, and Microsoft seems willing to sacrifice a few battles in order to win that war. Facebook is chasing virtual reality; Google wants home automation, smartwatches, and internet-connected glasses. More than 200 billion devices are likely to be connected to the internet by 2020, a huge example of the way the technology industry will shift and new battles will emerge. Satya Nadella believes the future isn't Windows desktops, Windows tablets, and Windows Phones. It's not Windows everywhere, it's Microsoft everywhere, offering software and services for every device - including an entire world of interconnected devices that have yet to be built.
The speed with which is doing this u-turn makes it quite clear that people within the company wanted to do this for a long, long time (otherwise it could not have been done this quickly), which implies that Ballmer may have simply held these changes back.
The elephant in the room here is that while people talk about Microsoft as if the company is down and out, it's still hugely profitable and has consistently been posting great financial results. It's just that Microsoft's money isn't coming from sexy products like smartphones and tablets, but from enterprise and backend stuff - stuff the technology press either can't write about, doesn't understand, or both. It's very similar to all those articles claiming Apple no longer innovates and disrupts, even though the company sent shockwaves through the microprocessor world.
In any case, it seems like Microsoft finally found the right direction in this new world.