JD, I think the reason is the cost of labour...It takes the bakers more time to cut a loaf into thin slices as compared to thick slices, and we all know that time is money, or in this case, bread.
Eh Sanmac? Bread is cut with automated machinery that have blades similar to that in a band saw set up next to each other. The setup is that a load passes through more blades to be cut thinly and less blades to result in a doorstep type loaf. Its nothing to do with time - the time is exactly the same if the loaf is cut thin or extra thick and everything in between. Sounds like your taking the Mick on thinking about it lol