Mendicate Bias,
Rare already had a handheld division long before they were sold to Microsoft. They've developed games for all Nintendo handhelds since the Gameboy Color, as far as I can remember. Secondly, Rare only developed two games for the Xbox, Conkers live and reloaded and grabbed by the ghoulies. The other games they developed where for the GBA, Which provided additional revenue.
Another thing to consider is that Nintendo Handhelds are very popular in all major territories. This means that Microsoft gets to target consumers who do not own an Xbox 360. For instance, Kameo, which is in development for the DS, gets released and has great sales. Fans of the game may want more and the only place that they will find more is exclusively on the Xbox 360. This could translate into more consoles sold.
Additionally, Microsoft may want to enter the Handheld market at some point in time. None of their first party studios know how to develop for a handheld except for Rare. Rare could provide their expertise to the other developers like Bungie who could then make a fps game like Halo or some other game tailor made for a handheld that deals with the limitations of a handheld, like the lack of processing power of the cpu, gpu, and the ram. And adjusting to a different control scheme. Remember when Microsoft wanted to develop avatars for the Xbox 360. They turned to Rare.



If Nintendo is successful at the moment, it’s because they are good, and I cannot blame them for that. What we should do is try to be just as good.----Laurent Benadiba







