I think it's worth making clear to you that we're all on shared web hosting, which means that there are many, many people on the same physical server using the Apache Virtual Host feature to have this same physical host used for many, many different websites. The way Dreamhost has this configured, we can many domains and subdomains to our hosting account. For each one, we configure a user and a directory to be the web root directory for that site.
Some people have one user and many sites. Some people configure many different users under their account with one site per user. Some people create usernames and give them to their relatives to use to host their sites. There are many options.
I'm not sure what techniques you're talking about here, but I'm hoping that my explanation above gives you enough insight into how things work here at Dreamhost and in the wonderful world of Apache Virtual Hosting.
BTW, for the record, you don't have to pay anything extra to host multiple domains here, you just have to pay if you want to register more than one domain. Also note that dreamhoster.com subdomains are free and any subdomain of any main domain that you purchase is also free!
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