I don't know exactly how Buck works (hehehe), but I would think in some (most?)instances, it is only specific IPs that get banned (and accounts properly), and only in extreme cases that entire ranges get banned.
If banning an entire IP range, one would have to find out what range an ISP use, before it being effective.
Banning a singular IP is much more effective these days then it would have been say 5 years ago, because back then most everybody used modems and dial-up connections, and it was very easy to change ISP. Thus somebody could effectively make sure that several ISP couldn't log on to certain boards.
These days more uses broadband and it takes much more effort to move ISP when talking about broadband/adsl.
Also - because of the usage of broadband the IP varries less then they did back in the dial-up days. An ISP only have a certain amount of IPs and they often have to be shared by a large amount of users (and between dial-up and broadband for some), thus I would imagine that certain IP(-ranges) are connected to a specific amount of users. For instance user group A will always be assigned IPs within range A. Although this is speculation but I've noticed that my IP changes very little, if at all.
Also - because of the immense focus on abuse, spam and other IT related "crimes", it is much easier to actual get ISPs to respond to notices about people misusing their Internet connection.
In Denmark I've heard/read stories about people getting notices from their ISP because they have been spamming up forums and similar.
So ... in short

- I think the need for banning entire IP ranges these days are smaller then they were a few years ago, and therefore I don't think that practices is used except in extreme cases, because you risk striking out towards innocents as well.