Dr. Pepper or Mr. Pibb

My boss and I were discussing these sodas the other day. I am not much of a soda drinker but last week we were in St. Louis and he was going into the gas station and asked if I wanted anything. He. came back with a Dr. Pepper. I pointed out his error and he told me, "does it matter, they both taste the same."

I don't believe they do. Thoughts?