If they are different how? They look so similar.

A replica is a replica...... now if you were looking at 18" RS6 5 spoke replicas... yes.. basically you could call it a b7 s5 5 spoke replica, couldn't you?

I think that the offset on the OEM 5 spoke in the S4 is ET 45, and the 18 inch RS6 replicas are ET 35, that may be the only difference.