You are talking like the brand means nothing, you know in the big picture it is important to count that too. The value of the brand itself is enough :)
Microsoft is investing in Xbox because the brand is now very well know. Microsoft will never let this go as one of their priority is to be the center piece of the living room. If Xbox One will not meet their expectation in that area, they will at least have build a good footing for the next generation. Not to mention Xbox Music, Xbox Videos etc...
You must look at the overall picture.
And as far as the rumors... They are exactly that: rumors.
i know the xbox brand is worth money thats why investors keep saying to sell it that its not part of MS core buisness, which its not. There was rumor last year that they(certain big investors) wanted MS to look and see if Samsung wanted to buy the XBox brand.