That isn't actually true. Sites can be, often are, double listed but the circumstances are strictly controlled. Generally you can have a listing in the Regional branch if your site has local relevance to where you are based. It may also be listed in a topical (i.e. non-Regional branch) if a category exists that fits the site. It may also be listed in Kids and Teens separately if it qualifies there. And it may be listed in each of the different language branches for which a translation exists on the site.

The help guidance is actually a little misleading on that one. It does say "You should submit your site to the single most appropriate category that is directly relevant to your site's content" but in http://dmoz.org/help/cats.html it explains about the others. It isn't a secret but it could be better signposted.

An interesting view but you have to understand the way DMOZ works internally. Firstly it would be patently unfair to deny editors own sites a listing wouldn't it. Secondly, editors always list their competitors at the same time as their own and none must be given any slant positive or negative - how an editor handles this is scrutinized very carefully. Thirdly every editor declares their affiliations so potential conflicts of interest are known and subject to monitoring. Fourthly, editors watch each other like hawks and there is no hesitation should an editor have a suspicion about another in hitting the Report Abuse button. There is nothing an editor hates more, even more than a pain in the *ss spam submitter, than a fellow editor who abuses their position. Put quite simply there is no tolerance in DMOZ for corruption whatsoever.

Maybe it would be useful to also give the top ten tips on how to get the most out of editors in terms of advice and assistance in submitting sites.

1) Be polite - editors are unpaid volunteers and are under no obligation to give anyone advice or assistance. They do so because they want to but if all they get in response is abuse then they will stop. Many editors have given up editing, others have given up communicating with submitters because of abusive attitudes directed at them.
2) Don't insinuate the whole of DMOZ is corrupt - editors hate corrupt editors more than anyone can possibly imagine. If you have a genuine concern and specific evidence, meta editors are waiting to hear from you.
3) Don't insinuate editors are lazy or neglectful - they have real lives, a living to earn outside, and are trying to build a resource in whatever spare time they have available. Your commercial concerns are of no interest or importance compared to reading the kids a bedtime story.
4) Read and grasp things like submission guidelines before criticising editors for failing to list your Nokia ringtones affiliate site.
5) Learn how to submit sites properly, to the right place, titled and described to standard, so editors can list them without delay.
6) Don't submit sites you know we won't let in, it wastes our time and yours, and don't then inquire about its status, wasting more time on both sides.
7) Don't threaten "legal proceedings" for the failure to list a site. To my knowledge no-one has succeeded to date after 6 years nor has even got as far as a courtroom. Frankly it just amuses us but if you want to pay $$$$$ to your lawyer to find out then go straight ahead.
8) Don't start spouting about rights - you have no rights over the efforts of unpaid volunteers.
9) Try and grasp that DMOZ is not a commercial listing service - we list sites, we welcome suggestions, we make no guarantees that suggestions will be accepted or when a decision will be made one way or another.
10) Try and work with us, not against us. Help us to help you by following the "secrets" I posted earler.