Here is the article that I saw:
Life sentences in white-collar cases are rare but growing more common, said Peter Henning, a Wayne State University law professor who has followed the Rubashkin case. "I don't want to say it's common - because it's not - but in the last few years it hasn't been unknown," Henning said.
At face value, it appears a life sentence prosecutorial request is (barely) within the bounds of current legal action...an outlier but not unprecedented. It certainly looks like the butcher made an awful decision not to take the plea deal he was offered.