It's not about what software stack is most well-designed, it's an entirely pragmatic way to look at things: to embrace the skills of Web developers to be able to create desktop applications for Windows with minimal effort. That's has to be the simple, obvious conclusion.
It also puts Windows ahead of iOS in the sense that it will become more Web friendly than iOS. Android is likely in the same boat as iOS in this respect.
This is embrace and extend for the Web.
Makes sense to me.