Hi,
Yes, we didn't implement the USPS plugin because we didn't have access to the documentation (USPS didn't want because we are not established in the US but in Europe).
With the API documentation, we would be able to make an official HikaShop USPS plugin
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.