Well, to me it's sorta like my walking out of the store without waiting for my change. That would be MY fault, but I'd sure appreciate the cashier running after me to hand it to me. I wouldn't expect an Abe Lincoln trek of 20 miles to return six cents (or however the story goes), but if I handed them a $20 bill for a pack of gum, I'd appreciate someone at least trying to get my attention in the parking lot! And I'd be the first one complaining if they charged me twice for something.
And I didn't expect a discount, but it was very nice and did make me feel good--not that honesty isn't its own reward.
I've always been pretty honest that way, but since I've gotten sober, the importance of it seems greater, somehow. It's that "rigorous honesty" AA drills into you.