In the beggining, Rare and Nintendo seemed to be good friends, they made kuncers togeather, banjo kazoie 1 and 2, and they agreed to put both kuncer and banjo in the racing game, Diddy Kong Racing. BUT lately Rare has been working with Microsoft in the game Banjo Kazoie Nuts And Bolts. And if you havent forgot, quite a while ago Rare made a game for the Origonal Xbox. And if you were to go to the Xbox Live Market Place, and if you go to Origonals section, you could buy Banjo Kazoie 1 and 2 for 10 Dollers.
Keep in mind, it's a company running a buisness, and first and foremost in that buisness, is the goal of making money. If Rare feels that they can make more money and do better paired up with Microsoft, then it's in their own best interest.
I suppose you could call it 'selling out', but in the long run, companies have to do what's best for themselves, and their employees. I wouldn't blame them for it.