As has already been mentioned, Ambassador status only confers gold elite status in the Priority Club program.

But being offered Platinum status for renewing Ambassador doesn't really surprise me. Two (non-Ambassador) family members who were not able to travel as much last year as in the past failed to requalify for Platinum status, yet were extended an extra (complimentary) year of Platinum status, no strings attached. Coincidentally, Delta also extended an extra year of elite status (FO) to these same family members. I assume that such actions as this are meant to maintain loyalty among past elite members.