I went to bed perplexed and woke up with the answer. It is not more air for efficient combustion as Jyden has said, this is a wrong conclusion.
http://www.oricpub.com/SE-1-1-2-3.pdf
The answer can be found by looking at the bsfc curves for different intake temperatures. See how the curves steepen downward at cold temperatures. Now imaging putting liquid nitrogen in the engine, it would run without any fuel. The gain in bsfc is due to the cold air expanding by heat transfer from the warm engine. This goes along with Nightking in that the engine needs to be kept hot in winter. The logic should follow on a otto cycle too, except for pumping losses may exceed the gain of expanding cool air in the cylinder.