Disappearing DNS-based Blackhole Lists

At about 4:30 PM (PDT) today, GreyStork and I were having a conversation about DNS-based blackhole lists, and we noticed something funny. The lookup addresses for quite a few blackhole lists suddenly aren’t resolving. So far, I’ve noticed that the following addresses don’t resolve:

Oddly enough, the websites for all of the non-resolving blackhole lists (which I’ve linked to above) don’t mention any changes or problems of any kind, with the exception of dorkslayers.org, which has a short message stating that the service is no longer available.

The above addresses are just the ones GreyStork and I had been using on our own mail servers. Some quick testing shows that many of the addresses listed here don’t work either. I’m pretty sure it’s not just my ISP, either, since the DNS lookup tool at DNS Stuff shows the same results.

What’s going on here? Is this some kind of sinister, spammer-supported attempt to fight back against spam blockage, or is this just a really, really weird coincidence?

Update: Looks like this may have something to do with it.

Another Update: This could have something to do with it as well.