If that's true then I certainly hope that someone at Sega cleared this with Nintendo.  Granted that Sega is its own company (mergers notwithstanding) and can do whatever it damn well pleases with its own creations, but if there is code being reused here, how does Nintendo feel about it being reused to create a game for competing consoles? There is a little history here.  Rareware walked off to Microsoft's sunny skies with several projects in the works for Nintendo systems, a few of which eventually changed into Microsoft Xbox 360 titles (Perfect Dark Zero and Kameo, incidentally).  There were concessions in the split.  In addition to money, Nintendo acquired a bunch of Rareware's characters that exist in Nintendo licenses (Krystal of Star Fox, the extended Donkey Kong clan, etc.).  Nintendo doesn't get part ownership in Sonic the Hedgehog if Sega reuses F-Zero code.

So if all of this speculation turns out to be accurate and Sega is legally able to reuse code in this manner despite it damaging the relationship with Nintendo, what could it mean for the future?  I'm just thinking aloud here, but Nintendo and Sega have become fast friends during this console generation.  There's even be a little talk about Sega's Yuji Naka and Nintendo's Shigeru Miyamoto collaborating on a Sonic/Mario crossover title, something that even just five years ago would have been mere fanboy insanity.  If Sonic Riders causes the Nintendo/Sega partnership to dissolve, then it had better turn out to be a hell of a game.