No, ntl customers are not flooding them, this is Slasghdot unable or unwilling to log the client IP. Because ntl broadcasts the client and cache IP, it is easier for Slashdot to ban the traffic server as opposed to dealing with the individual user.
Trust me, they do this often.
Tahe a look at this article.
http://www.cableforum.co.uk/board/sh...light=slashdot