There are two issues here:
1) The South African customs authorities will charge an importer according to the type and value of a good, as set out in the schedules to the Customs and Excise Act (or the Tariff Book). It makes no difference whatsoever whom you purchased the good from, hence it is a moot point whether it was purchased at Amazon, via MyUS etc. Amazon does not charge import duty fees, SA Customs do.
2) What are the duties? I may well be wrong, but as I understand it, a Blu Ray Player would not attract any duty, regardless from where it is imported, as this falls under §85.19 of Schedule 1 (Video Recording or Reproducing Apparatus). Vat, clearance fees, etc. would still apply.