According to sources, there were actually rumors of Jim Ross being let go by WWE a few days before it actually took place. On September 10th, the day prior to JR's release, someone in the WWE book department called an author to inform him that WWE had selected him to write JR's autobiography.
One source claimed it was odd for WWE to even publicize JR's retirement due to the fact that most casual viewers never see him on television anyways, and would already assume he had retired.
It was also noted by executives in the company that JR's release would have never happened as recently as a few years ago, and it's further proof that Vince McMahon is not worried in the slightest about TNA, in terms of competition.
Regarding JR's role as the man who worked directly with talents in the WWE NXT developmental system, early speculation is that William Regal will likely take over those duties.