You're correct.

It could actually be having an effect and I could just not be noticing it because there are many other variables in play.

I suppose my comment was inspired by seeing posts about soda and weight gain and seeing comments of anecdotal evidence for people who have cut out diet soda and notice their weight dropping significantly.

I merely wanted to provide an anecdotal data point (however useless scientifically it may be) to try and give a perspective from the other side of things.