Navigation Properties in Complex Types

[Василий Кудрявцев <vklava@yandex.ru>]

[OData-Part3] (CSDL Defintion) states:

As structural and navigation properties MAY be returned by the service on instances of any structured type, whether or not the type is marked as open. Clients MUST always be prepared to deal with additional properties on instances of any structured type, see [OData-Protocol].

In this light, I wonder, what is the reason tat complex types cannot declare navigation properties in metadata? I would serve a lot of real -life cases
For example, the Address complex type used throughout the documents is a bit unrealistic, as in most real cases it should contain a navigation property "Country", referencing another enitity, not just text representaion

-- 
С уважением, Василий Кудрявцев