That comment says: "memcachedb is not distributed, meaning that you can only scale vertically (i.e. by buying bigger machines)." Is that true? The docs on memcachedb seem to imply the opposite.
memcachedb is not distributed - it only supports replication. I.e. with memcachedb you can only scale reads, but not writes (or at least not without a system like LightCloud on top of it).