Defintely not a glitch. My 4 PS3 game orders were all done separately - at different times. I, too, logged in to the UK site with my US account. I was only denied when trying to order any 360 versions - perhaps Amazon 'knows' PS3 is region free (PSN codes aside)...
Thanks for bringing up this Amazon UK news. Hopefully this will make importing things a lot easier as I currently (rightly or wrongly) have more faith in Amazon than Zavvi and other sites. My US account was also imported, so it does appear to be a new policy. Vita games work too, so I assume PSP and DS games will be the same.
Also, when I did a test checkout, it appears that the final price is lower than listed. This could be because the prices on Amazon UK include VAT, which we are not charged?
Finally, does anyone know of any differences between the UK and US versions of the Ni No Kuni Wizard's Edition? Seems the UK version will have Amazon's DLC bonuses, but does it include the Ninostarter bonuses as well? I'm actually getting a cheaper overall price importing right now than from Namco's store, so I might actually go that route instead.