Yes... this sucks BUT.... Customs has ALWAYS been allowed to open ANYTHING coming from foreign countries. This is really nothing new.
I am sure since government staged 9/11 attack more packages get searched now but... anyone who orders gear from overseas KNOWS its a gamble when they place there order.
As far as DOMESTIC (USPS Postal) mailed letters or parcels... they CAN NOT open domestic mail without a search warrant. Thats a fact.
Fed-ex - UPS - DHL can open anything at anytime. Even when you place it on the counter to mail it ... and NO warrant is needed.
So, unless you are ordering something illegal from overseas, i wouldnt even sweat it.