I think there are ways around it? If i'm reading correctly. The loophole will probably closed soon enough I assume since it's a lot cheaper for EU to buy from US store.
Actually, this exploit has existed for years for their PC digital downloads, including games that rely on Steam activation, so I think there's actually a decent chance it might stay in place for PSN stuff too. Sony has some incentive to let it slide on their end; while it's still operating through Amazon as an intermediary, you're not forced to buy PSN cards from import sites that mark up their prices by 10-50% the listed value of the card as has been the case up until now, meaning that more money from "imported" PSN purchases stays in the hands of Sony and developers/publishers, rather than going to people making a quick buck off of a serial code, even if Amazon takes a cut from each purchase. On the consumer end of things, they get to save money by not having to pay for those mark ups, therefore enabling them to hypothetically purchase that much more content online. Given that the system as it currently is seemingly doesn't otherwise allow for region locking by design unless you buy PSN stuff through Sony directly, I imagine that they have a lot more incentive to turn a blind eye to this than to actually clamp it down.
Very much so hoping they roll this out for Amazon Japan soon. I know they already offer PC game downloads as well, so it would be nice to see this extended to PSN since Japan is warming up to game downloads since the 3DS' release. It would be extremely nice to be able to pick up some rarer Japan-only PS1 classics and a handful of PS3 games that way rather than spending half my budget on just paying a reseller $50 for walking down the street and picking up a card.