I think the main issue is that the business is still extremely profitable and has more than 1/3 of their costs tethered to falling nat gas prices.
Per the Q4 2011 conference call in Feb:
"Fourth quarter also provided a nice illustration of the way in which lower North American natural gas prices have raised our floor margins making our nitrogen business very profitable even in week periods."
"Our fourth quarter net income of $439 million or $6.66 per share included mark-to-market adjustments of $49.7 million before taxes or $0.47 per share after-tax. This represents the adjustment required to bring natural gas derivatives that will mature in future quarters to their fair market value based on the gas strip as of December 31."