RIA Services and Shared domainlogic??

Question

I'm kind of disappointed at Ria Services.

I like to work in a domain driven design way, so for example if I'm working with an invoicing system I have an object invoice which will have all methods on it to for example calculate total price from its invoice rows.

public decimal Amount
{
    get {return Entries.Sum(x => x.Amount);}
}

I like to have methods to add a new row to validate in data.

public void AddInvoiceRow(Article article, decimal quantity)

This is functionality I need on both client and server side.

Have I missed something big or is RIA Services not for me? (In the whole, I don't like Silverlight restrictions at all, I mean that we need get; set on every data field we want to transfer for example some fields are not public at all in domain driven design but the technique Silverlight offers forcing us to do bad coding.)