Different regional or national Origin stores vary in what they show as available, some things need specific searches to turn up (they don't show just searching on the words Ultima or Ultima Online), some things are simply not present on some national stores. As Aran says, their redirect system looks at where it thinks your PC is based on the IP address, and always forces you to use that regional store, and unless you use some form of proxy you can't get to any other Origin...
In summary - it's moronic. An international company like EA still seem utterly clueless about online commerce, can't cope with the idea that people nowadays move around the world a lot, and have some seriously bizarre ideas that some things should only be on sale in different regions for a game played all over the world. (The 'stopping fraud by selective sales on regional sites' whining is an outright nonsense, anyone using any web proxy can access any Origin store they like, and anyone even slightly serious about 'fraud' will know that perfectly well - although maybe EA, along with their demonstrated ignorance about the internet, do not even know that about that either).
They have shown no interest at all in sorting this mess out, despite all the 'we don't deserve our customers hating us' crying, and the pretend feedback surveys that keep pointing out the problems but then are just ignored (Cosmetic exercise to look like they care when they actually don't? Damn right.....) and their senior executives either never get told the truth about their awful systems, or ignore it because they are too focussed on the quick buck and the better selling 'other stuff'. They wont change because they can screw enough money out of the other products to cover over any minor potential sales losses on games like UO. Profits seem to be shooting up, from their last reported figures, so nothing will be changed because all they see is 'money NOW' and it looks just fine as far as they are concerned.
