I am really curious if Bill Gates seriously approves every Nadella's move.
I think this community puts too much stock in mobile. I mean, it makes sense that we would; we are here because we're Windows phone fans. But that doesn't necessarily mean that Microsoft lives and dies by WP. Microsoft's stocks have soared since Nadella has been in command. The stocks also soared under Ballmer.
Look at it this way; there are thousands (probably) of tech companies selling software and hardware across the world, and only two of them have widely adopted mobile OS's. If we say that mobile is crucial, how can we explain their success in the last several years with a barely used platform? Not only was it not accepted, it ultimately cost them many billions of dollars.
Since 2010 or so, mobile has become a smaller and smaller part of Microsoft's portfolio. I don't think it is necessary. Sure, they tried, but the public did not accept their offerings.
Microsoft basically said that they never did want to become an OEM. They were forced to by circumstances. However, as long as their services are being used, it probably doesn't really matter to them which platform they're on. I think the move with the S8 makes sense. Sure, it's not ideal, but given current conditions it's probably the best thing to do. And it costs them virtually nothing, offers their customers a mobile solution, and makes sure that their services are noticed on a best selling mobile device.
To directly answer the quote, I'm sure that Bill Gates doesn't approve of Nadella's every move. He probably didn't approve of all of Ballmer's moves either. In fact, I would guess that Gates himself when he was CEO made some moves he didn't like, but was forced to by conditions. But Nadella is CEO. He was chosen for a reason. So he diminishes a division that has hemorrhaged cash since its inception and saw little chance of a turnaround. It makes sense to me.
TL;DR Microsoft does not have to have a mobile OS to be successful.