Thats unfortunate that it causes you the hassle. But from the merchant's perspective, especially if they have been burned before, ship forwarding services are high risk.
Look at it this way. When you place your order, to the merchant, your IP will be from overseas, the credit card will be based in the US, and you are shipping to a ship forwarding facility. This is very typical of what fraud looks like with stolen US cards. The problem is that merchants bear the responsibility and chargebacks are a big problem, so they may not want to take the risk.
But the response does indicate whether the numeric portion of the street address matched and whether the zip matched. The merchant can choose to reject the order based on this information. In our case, we accept the order if either matches.
Many merchants also are looking at the IP location from which the order was placed. Depending on the country it may raise enough red flags to reject the order.
I ask because I live overseas and use a forwarding service quite a bit, but several smaller shops do flat refuse to ship to me, meaning I have to ship to my dad's and have him send it to my forwarding service, which ups the price a bit. And it's kinda frustrating, as I do have the address registered with my banks.
At least reading a story like this one explains to me a bit why things are the way they are.