I can't speak for other editors, but I know in the categories I edit the spam isn't being caused by me. We have a set of guidelines to follow when editing a site. If that site meets the requirements we're supposed to list it.
If there are many sites from the same company that look slightly different layout-wise, they still have to have different content or I won't list them. I do agree that the guidelines are a bit broad but I suppose in all fairness that they have to be.
If you think you see any particular editor/section that is very spammed out, please bring it to the attention of the meta editors and it will be looked into. But what you might be seeing, especially where free sites are concerned, are sites that actually do meet the requirements and therefore must be listed.
If you could see the amount of stuff I delete in one day you'd be amazed. People will try any angle to get their sites (doorways, jump pages, you name it) listed in the ODP. So believe it or not, the real spam rarely makes it into the directory. At least in my experience.