The rationale I have had from The New York Times is that they commonly use the word "retarded" because mental retardation is still a diagnosis in the American Psychiatric Association's (APA) diagnostic manual (DSM). In fact, I've done a search and realized that describing someone as "severely retarded" is common practice at the newspaper. Here's another recent example:
Thanks to another blogger I learned that the APA has proposed a name change to the current diagnosis. They plan to change the name from mental retardation to intellectual development disorder in the updated DSM in 2013. I have sent this to the the public editor at The New York Times.
If you click on Rationale, it explains that the name is being changed because the term mental retardation is no longer used internationally, or in U.S. federal legislation.
1. Name change. The term mental retardation was used in DSM-IV and in earlier DSM definitions. Mental Retardation is no longer used internationally or in U.S. federal legislation, so a name change is required in DSM-5. The term Intellectual Disability (ID) is widely used. This term is used by the AAIDD and criteria have been developed to define ID as a functional disorder, explicitly in keeping with the WHO International Classification of Functioning (ICF).
Which leads me to question why an authoritative paper like The New York Times would drag its feet?