I used to work for a computer parts importer and they had contracts with the delivery companies.
Basically, we managed to secure a 5 year contract, for a flat fee for each package regardless of the size. The downside was we had to prepay in advance the shipping dockets that we would attach to the packages.
But we could charge the customer the actual shipping cost that was listed on the shipping docket, but in fact, we initially paid for a lower cost.
We made a profit each time a customer ordered something.
So you can see, maybe HP has a contract with the shipping company for a reduced fee because they used their services so much.
So, if the packaged was listed as $XX to be sent, in fact, HP probably only paid a small percentage of the shipping cost.
So keep in mind that when they say $XX for shipping, companies are making money on those charges too, and don't buy the bull about, it cost us this much to send something because the shipping company charges us these amounts.
They most likely get special rates from the shipping companies.
We used 3 companies initially for shipping, but they would outbid each other to get our business that at the end, we settled on one company exclusively.