Did you ever have to stand on your tippy toes to reach your favorite brand on the top shelf? There's a reason for that. Grocery stores (and other stores; I won't just pick on grocery stores) display the most expensive items, and the ones with the most impulse appeal, at what is eye level for most people.
Surprising? It shouldn't be. We need to be aware that all stores do everything they can to get us to buy as much as possible every time. That's the name of the (marketing) game and we play it whether we know the rules or not.
Products on the lower shelves often appeal to children, which is a good incentive for keeping children in the shopping cart! Generic products are often down there, too, so they don't compete directly with brand name products which are, of course, at eye level.
The next time you go into a grocery store, compare the prices of the items on the lower shelves with those on the middle to upper middle shelves, then compare those with the prices of items on the very top shelf. Do it in several different areas of the store and see what you come up with.