The actual cost to move packages from bulk shippers (even internationally) is very small. It is less than $5 per piece for a package of small size. For something like computer products, the cost of air cargo to move them is so small relative to their "value" that shipping cost to move the product (even to an individual consumer) is a very small percentage of the total value of the item, often only a few percentage points of the value. Shippers such as Apple will absorb this cost in order to offer "free shipping" to consumers (making up the cost in slightly elevated product pricing or slightly diminished margin).
The discount scheme FedEx uses for high volume shippers can be confusing, and when one compares their discounted price to full over the counter rate - actually shocking. The highest volume shippers only pay what amounts to 20-30% of full over the counter rate (they get a better deal than Express employees do in shipping, so much for "employee" discounts). The US federal government receives the best discount, it is close to 90% off of full rate. The US government pays less to ship something overnight than it would cost someone to ship the same item via USPS Parcel Post.
I've seen discounts for customers (at Express over the counter sales), that after their account number is entered (and their particular rates are applied) come up to over a 80% discount - and the customers KNOW the discount they are receiving relative to everyone else.
This is why when people asked me, "How much to ship this item by Express?" - my first response was, "Do you have an account with a discount applied to it?". They always answered no and I responded with, "Ship via USPS Express Mail if you need it there overnight, you'll save a bit".
Most people don't have a clue as to what full over the counter rate for overnight really is. They think $10-15 to get an envelope across the US - it is more like $25-35 over the counter rate.
The over the counter rate is the baseline for FedEx when it comes to negotiate rates with shippers. Then sales will analyze the volumes offered, the cost savings realized with bulk shipments then make the big analysis and try to figure out what UPS is going to offer in terms of actual shipping costs. Then a percentage discount is offered to the standard rate schedule.
When one time bulk shipments are to be made, these shippers will contact all potential carriers and get a quote. Sales will do a very quick analysis of costs involved, spare capacity in the line haul network (if there is spare capacity, incremental costs to move the volume is close to zero) and whether they want to develop a "relationship" with this shipper - then offer a one time rate schedule. Most of the time, these schedules are priced at a flat rate per piece moved, and don't utilize zone pricing or require the shipper (or Express) to actually weigh each individual piece. They know the average weight of the pieces to be shipped, so they flat rate the quote to a per piece cost (say $10 for each piece tendered in China to get it delivered to any address in the US).
This is why people get all confused when they go to ship something Express and get charged the proverbial arm and a leg, but can't understand how they got "free shipping" to receive an item of like weight in the recent past. Volume determines rate schedule - if you don't have the volume, you pay full rate.