The "www." subdomain was a generally accepted convention -- but never a standard -- back in the early days of the web: when people had separate servers for e-mail, FTP, gopher, and so on, and used the "process server type" as a convention for the subdomain name. But when HTTP became the most common kind of service -- and as server software (and corporate sysadmins) became more professional -- most serious sites abandoned the now pointless "www.", except as an alias for their new single point of connection to the internet for backwards compatibility.
The problem enters when webmasters (or their users) forget whether the www is allowed (or as in occasional seriously botched configurations) required or even occasionally forbidden. And then we get -- as you see here occasionally -- "www.dmoz.org" versus "dmoz.org". Well, if the sysadmin gets the aliasing set up correctly, there's no problem, either for us or for Google. And that's the CURRENT convention (although still no standard). Most sites treat the www. as meaningless -- as good a reason as any not to include it -- and that's how the dmoz server software treats it. (The exact mechanism of that treatment is mysterious to me.) Google is also pretty good -- but not perfect -- at figuring out the equivalence, although it's sort of random about whether the wwermiform appendix is the canonical URL.
Which brings back another hassle for us. People who were careless about whether or not they included the www in their own published URLs, then have the random choice of alias chosen by Google -- rather than going back and whacking their system administrator with a clue stick and getting the redirects done right, they submit pointless URL change requests.
Of course, if you're consistent with wanting everyone to type the four extra characters, it's not really a problem to the ODP -- just a minor distributed annoyance to the people who have to type the extra characters, or forget you have to type it because most websites don't need it anymore.
