I just noticed that when you select an iMac on the Belgian Apple Store, you go directly to the page "Clients also bought.." list of accessories.
http://store.apple.com/be-fr/browse/home/shop_mac/family/imac?mco=MTE2NjM
("Choisir")
You apparently can NOT change the RAM amount or upgrade to another video card!
as it is possible on the French or US apple store...

EDIT: it seems it is possible for the first iMacs but NOT for the highest machine... Strange.
http://store.apple.com/be-fr/browse/home/shop_mac/family/imac?mco=MTE2NjM
("Choisir")
You apparently can NOT change the RAM amount or upgrade to another video card!
as it is possible on the French or US apple store...
EDIT: it seems it is possible for the first iMacs but NOT for the highest machine... Strange.