If you read the Wiki article you linked, you would know that ammonium phosphate is a more effective fire retardant.  In addition to the heat of vaporization it also envolves an endothermic reaction, sucking heat out of the fire. Another benefit is fertizlizing the soil, aiding in regrowth after the fire. 

I would also point out that you failed to include the '[source needed]' with your quote.