LOL, what makes you think it's rubbish? Talk is cheap, can you back yours up? I know you aren't an editor with first hand experience or you'd know better.
I use to check from time to time, then again I was quite familiar with my niches few things would slip by unnoticed but since I was removed nobody will care about those categories ever again so I'm guessing it is pretty safe to exploit them. I did few of those in my days about websites I was about to delete to make sure they are really gone forever not just having server problems.
Not annie but I may try and field this for her if its ok. For the most part its random I would guess, editors working on general maintenance (ie checking links, correcting typo's etc) may notice something that draws their attention and check. Other times its an update request from someone such as a customer that knows the company changed hands. There would have to be something to initiate the checking process, it doesn't just happen automatically unless of course as I mentioned the editor is actively checking things in that category at the moment for any problems or errors. Yes many editors make sure to look at this information whenever possible while they are reviewing sites. Do they have time to always do it? Probably (most likely) not, but then they are also not always reviewing sites and for me I typically check this information when I am looking to clean up a category. Something flags it as needing to look closer, either a public submitted update request or something on the site or within the link that spike curiosity. And yes it is useful to those trying to keep the category clean of useless, dead, hijacked and otherwise irrelevant sites.
Many editors check the whois information, but a change of ownership for a website doesn’t mean that the website is automatically unlisted. I also check the whois information among other Dmoz tools when reviewing websites. One day I happened to find three sites in different categories I edit with new owners. Site A’s new owner actually put up better content than the last, so the site stayed. Site B turned into a page full of just affiliate links and adsense, and Site C redirected to spam, so I tossed out Site B and C. If a new owner still provides the same content, there is not a need for an editor to delete the listing.
One example of a DMOZ tool - a domain nearing expiry and not renewed gets removed to Unreviewed and an editor has to go check it before it is restored.