not2easy - 2:26 am on Dec 12, 2012 (gmt 0)
The lists don't stay static. When the bots find themselves ineffective because of the number of entities blocking them, they move. The number of servers that want to host unsavory operators is not unlimited so they do sort of gravitate to certain servers that you'll find discussed here. If you add other methods to this it is more effective.
I use a trap I got here in WW Forums to catch robots that don't follow robots.txt instructions and use those to look up IP ranges to block. I get others from this most helpful forum and use my access logs to see who is misbehaving and needs to go away. If you are using Mac, there is a handy app that gives you whois services. You will have a more useful list if you build it yourself but even your own list needs to be updated once in a while.