The Submittal Policies don't talk about not submitting "not-different" sites.
They talk about not submitting "related" sites.
Sites such as you describe are on a similar topic from a similar source. According to the submittal policy, submitters MUST treat them all as a single suggestion.
This is for the editor's protection. You can probably imagine how many self-serving webmasters create lots and lots of tiny sites to try to get better visibility in the search engines and directories. (Experienced editors don't have to imagine: we've seen them!) So this policy is enforced rigorously: more rigorously than required for the SURFERS' good, because it's needed to protect the editors.
And yes, the policy will affect some innocent website owners who arranged their domain names ignorantly, without malice or deceit in mind. But look at it the other way: the policy encourages website owners to integrate all their related content--so that a surfer who finds any part of it can stumble into the rest. Which is indisputably the right way to do website navigation anyway.
Do the navigation right, and it won't matter that there's only one link into the material--all will be visible at that one place.
And once THAT concept is grasped, then the realization that what's unique about YOUR site is that YOU put it together, not that it contains information on whatever particular subtopics you chose....ALL websites are ultimately personal. And the idea of having separate domain names for each separate subtopic, which aren't tied back to YOU, YOURSELF (the branded element) can be seen as the fallacy which it is.
And once the website is clearly unified by a common domain name, then the ODP editors can be more comfortable about tracking "related" material--and therefore more comfortable about deeplinking different subpages of the site.
Because a single site is MORE valuable than a group of "different but related" sites with exactly the same content....and it's often more worthy of multiple listings in a directory, NEVER worthy of fewer listings.
Yes, I know, this is not what the spammers tell you. They say, have a hundred sites, and when one con is spotted, you can continue the others undetected. But this is the way the honest part of the web works.