Thanks for all the WAI feedback.
This warm air thing seems to have no one single answer.
Here is my current summation:
The greater the temp of the air, the lower the density.
Lower density air has less molecules per volume.
Less fuel is needed to keep the 14.7:1 ratio of air to fuel.
Also, the WAI could just be explained away as magic. That is usually my answer in an arithmetic class. Stumps the professor every time . . . 
