Now: Nuance was spun off of SRI probably a decade or more before Siri was birthed in a Darpa program called CALO. CALO may have, in some implementations, used EduSpeak or it's lightweight cousin, Dynaspeak. But I'm pretty sure that when Siri was ALSO spun-off from SRI, and bought by Apple, that Apple did not want to pay the license fee for the EduSpeak code. So they used something else (which, AFAIR; was an Apple-confidential matter).