Here are two statments from Mark Rosewater, the Un-rules manager:
http://markrosewater.tumblr.com/post/69926019862/why-dont-silver-bordered-cards-ever-recieve-oracle
My understanding from these replies is that the Un-cards should be played with the Oracle updates, that they simply have not gotten around to posting the updates.
I don't have the Reputation required to post the links indicating that he's the Un-rules manager. If that's in disupte I can post them in the comments.