During some of my free time I have developed a theory as to why you can receive FM using AM demodulation. This theory uses a little bit of physics and also some thinking about different ways to plot signals.

First most of the time when we see a plot of AM and FM signals it is Amplitude plotted against Time.

This is how we can see the Amplitude of AM changing and the Frequency of FM changing. But what if we decided to plot them Time against Frequency. We see that AM is basically a straight line. While FM moves about left and right of its center Frequency. Now lets think for a moment if we placed a box over part of the FM signal. We will see that the signal crosses this box. The lines in the box can be looked at as the area AM would see. The lines in the box are a higher Amplitude then the areas with no lines. The Amplitude indeed is modulated bu the fact that the Frequency is changing. This changes the spacing between the line in the box which is a change in Amplitude. I will enclude a few picture of what I am talking about.