I'm not aware that there are any plans for the US e-store to ship overseas. If a product has been launched in any given territory it should be easily available from high street retailers or from other online retailers. If you're thinking about the Rio Receiver or Rio Central then those products have not officially been launched outside of the USA.
Lots of retailers don't accept American Express, including some of the largest retail chains in the UK. This is probably due to - shall we say - the less than attractive terms that AmEx offer to retailers.