I didn't know that, interesting ^^ (I just tried to go to amazon.com and read their terms and conditions, but I couldn't even connect.. :P Connection is so crap from here)
Again some of my substandard translation...
Overseas delivery restriction(s)
In some countries, due to their customs (government agency), adult and religious books, as well as DVDs and video, etc produced in Japan may not be able to be delivered. If that happens, we will contact you and cancel your order, please understand, Also, the only items that can be delivered overseas are, with the exception of all adult material, books, CDs, DVDs and VHS. All other items cannot be delivered outside of Japan.
Guess some foreigner got caught with their pants down fapping to loli eromanga... Or something (i have the sneaking suspicion that if it was shota material they would do a better job of concealing their activity)