This is because, after years of analysis of how humans move in a store, they've found that we're as easy to predict as animal migrations. Studies show that Americans like to shop counter-clockwise. Over time, they've found that stores that cater to this by putting the door on the right do better business than stores with the door in the center or, worst of all, the left.
Grocery stores are laid out to lead you around a set path you didn't even know you were following. Knowing you'll head right, they place the freshest, best-looking stuff they've got right in your path. Not the most popular stuff, mind you -- they know most of you didn't run to the store at midnight to buy lettuce, and they know that if they put the Doritos to the right, you'd grab them and head to the counter. Instead, they lead off with the produce, which tends to make the best psychological impression on you. The idea is that you'll associate the rest of the store with the freshness, bright colors and nice smells you got from the nicely laid-out produce.
"Boy, those fresh carrots sure did help me forget that everything in this aisle has been dead for weeks."
After they hit you with the brightly colored lemons, apples and oranges, they schedule your predictable counter-clockwise path so that different products show up at the exact time that will make you most likely to buy. The stuff you actually came for -- cola, chips, milk, eggs, sliced cheese, cookies -- doesn't show up until the end, once your cart is chock full of stuff you didn't know you needed when you walked through the automatic doors.
And sweet lady Boxed Wine.