Dmoz is a human edited open directory, all dmoz editors review each and every submission before accepting them, same for Zeal also.
It's not a search engine. DMOZ.org has different results than DMOZ.com. How often they update their servers with the new data is up to them. After being accepted into one of the categories the search results page does not automatically update with the new data. -Same with deleted sites; the data still shows up. DMOZ just relies on the people's kindness to edit. It may be a bit of a cynnical viewpoint but I think the system works fine -just people in general just want to take and not give back. Because of the massive scale of links it provides to sites like alexa or php includes of the directory, it's not good to have it constantly changing and moving the links around. It's best just to keep consistently updating over a set interval to ensure quality