After reading this aloud to another developer I agree the wording needs some work. I'll try to re-word this tomorrow when I'm less sleepy. 

My rational for including this is it was not immediately obvious to me the benefit to setting the jqXHR's `then` property to null. Since the adapter is only used internally and users are encouraged to use the `store`'s api for query for objects I assume this documentation will mostly be consumed by someone looking to extend the `RESTAdapter` class. I thought it might be helpful to note why it was important that the `then` property be set to null so developers could make informed decisions about calling `_super` when extending the `ajaxError` method.