I think the author is maintly talking about home or small office use. I don't know of any large organization that uses Outlook and stores the email on the local workstation (too difficult to backup email on the local workstation). When this happens it is usually a user that creates a PST and moves email into it.
All the email protocols allow you to keep email on the server, but the default setting for all except for the exchange protocol default to removing it off the server.
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