From what I've heard on DSC (Adam Curry), it is based on your credit card. For US access you need a US CC.
I was listening to the podcast and it was discussed about whether someone outside of the US could get these shows. Basically, nope. I tried to purchase music out the the EU and was denied. You can change your location in your profile, but that may not help.
I was living in Bermuda and I was only allowed to purchase from Canada. So I don't think this is IP-centric as it may be thought. I am investigating this as I am not in Bermuda or Canada anymore, so I need to find out what I have to do to change all this.
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