One of the major arguments used by Riverbed is that it provides a single data store for all peer devices on a steelhead appliance, whereas WAAS creates separate data stores for each peer.
Is this still the case or not?
You are correct and this has not changed. I've been involved with deploying WAAS since it was released by Cisco and have heard that as a line for years in the marketing FUD fliers being sent around.
From a technical perspective, in my large deployments of 100s and 1000s of boxes, this really hasn't been an issue to date. It is just that, FUD...