This makes perfect sense, seeing as how Nokia's smartphone line has been a big supporter of the WIndows Phone platform. With the company's Devices & Services division under Microsoft, you can bet MS will use this to beef up its efforts in competing against Apple and Google.
Stephen Elop, the current Nokia CEO, will head up Microsoft's "expanded devices team." When Elop takes over, Julie Larson-Green, the current head of Devices and Studio Engineering will work as a member of his team. This means that Elop will be taking charge of the new division, not the least of which includes the Xbox platform.
Expect to see a whole lot more change at Microsoft now that CEO Steve Ballmer has announced his retirement.