Isn't this a very sneaky way of getting people to register on their own regions now? My account has always been on the UK region for many years now due to legacy issues with XBOX Live in the past (it being not available in SA was a pretty big contributor). Also, I've never seen the benefit of migrating my account to the South African region since it didn't offer me anything new in terms of store content. In fact, the SA store is usually way behind.
So now, since we're not working with points anymore (which were region free) - you have to migrate or register on your actual region, otherwise your credit card won't work with store purchases.
This is total BALLS in my opinion for 2 reasons:
1. I don't want to be on the SA region/store since the content is lacking compared to the US/UK stores.
2. I don't want to use my credit card for MS/XBOX purchases since Microsoft links your credit card details PERMANENTLY to your Live account. It's not like the Playstation network that allows you to remove your credit card details immediately after a purchase. So with Microsoft, if someone ever manages to hack the "MS Live" network - they'd have your credit card details as well since Microsoft keeps them linked.