Can consulate require a cosponsor when current income is more than 2 times poverty guidelines?

I am looking for an answer to a specific situation. I am also looking for case law examples to back my case. My wife had her interview in Guangzhou, China. She was asked many questions about me: Whether I am still employed (I am); my age (69); etc. Her visa application was preliminary approved. However, she was inexplicably requested to get a co-sponsor and provide appropriate tax returns. My I-864 shows my income for 2014 at $76,824; for 2013 at $60,554; and for 2012 at $56,624. This is more than double the 2015 poverty guideline for a household of 4 (which includes an adult adopted daughter, living on her own who also sponsored by me). The guideline amount is $30,312. Can the consulate require this co-sponsor? I do not want to place anyone else into a legally binding contract with the Federal government to support my wife and son. Speculative positive income cannot be considered for I-864. Can speculative reduced income be considered to require a co-sponsor. I fear there may been prejudice against us due to my age. I have not retired. But yes, I may retire in the future. Can the Consular officer use this against the present facts to make this requirement of a co-sponsor. Because there was no explanation from the officer as to why this requirement was established, I can only go by the facts and the nature of some of the interview questions. I am also only speculating. The facts support our visa application, yet further requirements were established. What case law is there to support our case?