As far as why some IPs don't resolve to a host, occasionally, the lookup just fails. I'm assuming that it generally happens when a server is down somewhere along the line. The ones that NEVER resolve, could be anything.
As far as strange IPs like those, I've seen one on a MUD I code at, yes. k197 or something like that. I don't know if the player plays there anymore or not, don't think I've seen him in a while.