That's not quite true because  is undefined, not 1.

But any other number to the zero power is indeed 1.

The reason it is 1 is because you can take any non-zero exponent,
say, 7, and consider this:



That must equal 1 because when you divide a number by itself,
you must get 1. So



Now if the law of subtraction of exponents is to hold true, then
if we do that same problem by subtracting exponents we get



So 

Edwin