Though people do it frequently, it is very inaccurate to compare volunteering with the ODP with volunteering with most non-virtual organizations. ODP editors do not sign up and are not accepted with the expectation that they will review suggested sites in x weeks/months...or even at all.Now back to DMOZ, people submit their sites, they fill in the forms and try to do everything correctly, by doing this they expect that somebody will look at their page within a reasonable amount of time (2 weeks to a month).
Now the editor who's also a volunteer agreed to edit and review webpages in his/her free time when they feel like it.
What happens here is that the DMOZ editor doesn't show up in the "soup kitchen" because they don't look at the sites people submitted.
That's why people get mad, you don't deliver the soup, well eventually you will in a year or two or more.
You might compare the ODP (favourably or unfavourably, depending on your POV) more accuragely with Wikipedia, where people can choose what articles or what parts of articles they edit at any given point -- they can spend as much--or as little--time as they choose doing whatever they choose as long as the net sum is an improvement in Wikipedia. Today it might be updating a link or correcting a typo; tomorrow it might be writing a full article. *That* is the way that the ODP works, except that the number of people who can edit any given item are more limited in the ODP.
So, there's no ODP soup kitchen and no volunteers who promised to appear on Monday at lunch to dish out soup to the hungry.