So the Chinese set the rate that they pay to have the USPS deliver stuff? No
>wonder they often include free shipping!
It's even more insidious than that. The Chinese govt subsidise outgoing postal costs (it's about balance of trade to them) and that makes it even easier to offer free post for China exports.
One electronics parts source elesewhere in Asia (I won't mention the name or country) have sussed this out and use it to their advantage. The greater part of their outgoing is almost invariably padded envelopes and small parcels. These they aggregate into a v.large parcel and send to their agent in China, who breaks the consignment out and re-ships individually with the subsidised China system.