I am sure you also like to point out that when people are using cash, they are "really" exhanging rectangular pieces of cotton/paper/plastic.
Granted, many understand that and are perfectly fine with it as you're helping to effect change. However, a lot of folks have been really confused by that marketing line, so it deserves clarification. HN users are probably more educated than the general public of course, but I work in this industry and strive for clarity.