It's a bit tougher online because shipping costs can vary a lot depending on where the customer lives and what they're buying.
For example, the cost of shipping me two boxes of cereal is barely higher than the cost of shipping me one box of cereal. The cost of shipping it to Alaska is much higher than the cost of shipping it to New York. In a store, the cost of getting two boxes of cereal to the store is, on average, about twice the cost of getting one box, and the cost is identical whether your customer is from New York or Alaska.
Your store scenario isn't true at all! It does not cost about twice as much to get two boxes of cereal into a store as one box. The same shipping economies are in play here. It actually costs less per box to get it into a store because they will bring in a pallet at a time. The real cost is the fact that you have a building and all of its costs with employees and all of their costs, etc. Shipping anything to Alaska is more expensive that to New York whether it is one box of cereal or a pallet. The difference is that the price for a box of cereal in Alaska will have that priced in vs the box in New York. The same can be done for online retail...except people won't understand it and get pissed and try to change their location reporting to try and get a lower price based on where they are located. You see, people don't view online shopping the same way as they view physical shopping. People will need to be reconditioned about online shopping now that we have the technology to do location based pricing thanks to geolocation reporting and other factors (like getting a zip code up front) that were not available when online shopping first came about.
It is only double if you are receiving cereal one at a time: but with distribution centers and things like that, it is rarely the case.
It is likely, if you are ordering one box of cereal, that it is packed in a box with other things and that you get the box with your normal delivery. Heck, with this model, even getting two lawn mowers along with the shipment doesn't change the pricing all that much.
You basically have the same shipping for all 8 boxes of cereal on your shelf.
It is much more true when you ship to consumers - the cost is nearly double if you are sending the 2 boxes to 2 customers. Gotta have separate boxes with 2 labels, because they are going to two houses.
For example, the cost of shipping me two boxes of cereal is barely higher than the cost of shipping me one box of cereal. The cost of shipping it to Alaska is much higher than the cost of shipping it to New York. In a store, the cost of getting two boxes of cereal to the store is, on average, about twice the cost of getting one box, and the cost is identical whether your customer is from New York or Alaska.