In addition, you will always be in a volume game no matter what OS you have. Most of the Win Phones don't even have the Windows logo on them aside from the main button. So it's not like Microsoft is using Windows to market the phone. If anything they are going to great distances to minimize the focus of their brand. Why? Probably because you can't play a game of volume if you have none to begin with. Microsoft in those markets is like Chery competing with Porsche. Now could Chery be known for building supercars? Sure, some day. But they surely aren't known for it now. So what is the brand buying you in a market no one associates you with? Well nothing. That's why Microsoft needed Nokia and not the other way around. The underlying OS on a Nokia phone can be anything and if it's good enough people will buy it.
The only problem with that move however is if you bundle a good brand with a brand that most people can't stand. This is what you have with the MS and Nokia relationship. People will avoid Microsoft at all costs if you give people a good valid alternative...and there are tons made by HTC, Samsung and Apple...on Android and iOS that is.