I believe Nintendo got to keep the rights to anything Diddy Kong related, I could be wrong.
yep, found this..
Rare is a company familiar to Nintendo fans everywhere, having made Goldeneye, Diddy Kong Racing, Donkey Kong Country, Starfox, and many other classic Nintendo titles. Starfox Adventures is said to be the last game Rare will produce for Nintendo, and while Nintendo will retain rights to the Donkey Kong, Diddy Kong and Starfox series, Rare will keep Perfect Dark, Conker, and Banjo-Kazooie, and will likely develop future X-box-based sequels.
No diddy kongs on 360