That could be the explanation, different forms and services being handled differently.
If they only knew how much small valuable stuff crosses borders without any customs forms. My local post office sometimes would tell me my packed item was too much like a letter to need a form. I usually filled out the small one anyway. But I've recieved stamps that were sent in letters or greeting cards. I haven't been charged duty on any stuff I've bought from overseas, maybe USPS is just too lazy or overworked to bother?
Funny thing dealing with customs. A friend of mine bought a big batch of films from Australia. Since it came into Boston as freight he asked if it was worth the price a customs service wanted to "clear it through" Something like $250. I told him we'd do it ourselves since it was local. At customs, the clerk told us the film wasn't a duty item, but the 2 basically junk projectors were. A few thousand in films, and essentially crate filler of projectors. And the shipper hadn't broken out the value. After they had a bit of talk back and forth I offered the thought that perhaps the customs clerk could solve the value problem by assigning a value that customs would find acceptable. After a brief bit of math she assigned a value of about $500 to the projectors. Total duty about $75. My friend asked if I thought that was fair and I told him to pay her before she changed her mind and assigned the full value of the whole shipment. I've seldom seen Govt paperwork get finished as quickly nor a Govt clerk actually seeming happy while filling out forms.
The whole thing took less than an hour including loading at the terminal.
Steve B