It's basically a UI problem: while you can authorize content from multiple regions, updates and subscriptions require actually being logged in to the iTunes Store, and you can't log in to multiple regional iTunes Stores at the same time.
I suspect one of the reasons Apple hasn't "fixed" this is because doing so would require renegotiation with content providers, who'd most likely push for even more customer-hostile restrictions.
I think there may have been some misunderstanding here regarding his App store account though; I also see a comment on his blog indicating this. I moved from Europe to the US and can't remember having any problems moving my account to the US. I can imagine that it's problematic to have two accounts on the same device though.