Networth example with ldp:contains

hello, 

Following up on the long call this afternoon ...

In the following two examples, where/why is it necessary to use client preference for materializing ldp:contains ? 

1. 'DirectContainer' case (such as a Networth in the spec): 

<>
   a o:NetWorth;
   o:netWorthOf <http://example.org/users/JohnZSmith>;
   o:asset 
      <assetContainer/a1>,
      <assetContainer/a2>;
   o:liability 
      <liabilityContainer/l1>,
      <liabilityContainer/l2>,
      <liabilityContainer/l3>.

<assetContainer/>
   a ldp:DirectContainer;
   dcterms:title "The assets of JohnZSmith";
   ldp:containerResource <>;
   ldp:containsRelation o:asset.

<liabilityContainer/>
   a ldp:DirectContainer;
   dcterms:title "The liabilities of JohnZSmith";
   ldp:containerResource <>;
   ldp:containsRelation o:liability.

POSTing to  the LDPCs (<assetContainer/>, <liabilityContainer/>) creates new Assets and Liabilities. 
The response has the Location: of these newly created resources.
If I GET the LDPR, I see domain-specific <asset> and <liabilities> triples.
If I GET the LDPC, I see ldp:contains triples. 


2. 'SimpleContainer' case:

<>
   a o:Box, ldp:SimpleContainer;
   o:boxOwner <http://example.org/users/JohnZSmith>;
   ldp:contains
      <item/m1>,
      <item/m2>;

In this case, the LDPR and LDPC are the same thing, and by the ldp:contains triples are found when GETting. 
There isn't a duplication issue. 

Roger