Why do I have to call SetLink()?

Question

I have some Linq to WCF DataService code that looks like this:

Account  account  = Account.CreateAccount(1);
Employee employee = Employee.CreateEmployee(1);

context.AddToAccounts( account );
context.AddToEmployees( employee );

employee.Account = account;
context.SetLink(employee, "Account", account);

context.SaveChanges();

This is working, but why must I call SetLink()?

In my example the call to SetLink() is nearly identical to the line above it.

Why can't assigning the account object to a property of the employee automatically call SetLink behind the scenes?