The passthrough is due to the fact the AGL owns the transmission and wholesale capability. These are the fixed costs. Think of it as the same thing as paying UPS to deliver a package that contains something you bought online at Amazon. You pay Amazon for the product (in this case the natural gas from your provider) and the transmission is paid to UPS (in this case AGL).
It's not a perfect analogy, but close. My gripe is the fixed monthly charge of $5.99 that I pay my supplier GNG just for having the good fortune of being able to buy natural gas from them. Add to that my actual usage at the associated per therm cost.
Unfortunately, complete deregulation in utilities is usually not good for consumers. I agree with the free market theories it's based on, but natural gas and electricity are not widgets, and the barriers to entry are very high.
In MA, during the summer, my natuaral gas bill was something like $12, which was what I spent for hot water. No fixed fees or services charges, but of course the flip side was that I paid the price I was charged, no matter what that was, and if I didn't like the provider I had no choice.
See the FAQ:
Georgia Public Service Commission