True, but DIDs are more flexible. For example, if a vat is identified by the hash of its public key, existing sturdy refs are invalidated when the vat changes its key. That won’t happen if the sturdy ref identifies the vat by a DID with a DID document listing the new public key.
Also correct. I didn’t think the scheme would work fast enough not to break things, so I tested it at HP Labs by taking my laptop from one WiFi subnet to another one while running a waterken program. I couldn’t tell that the machine’s IP address had changed.