TfL likely need that mechanism primarily to synchronize the list of blocked open-loop bank cards with unpaid balances to all readers. Faster Oyster transaction list updates and any-station remote top-ups are probably just a side effect of that.
Clipper doesn't (yet) support open-loop bank cards yet, so for them, it's probably enough to update more remote readers every time the bus goes back to the depot, for example.
But yes, for speed/redundancy they are still probably using the stored value balance too.