To cut a very long story very short... most ads come from the same sites and are linked to in the page rather than actually embedded in the site. This is how the site owners can get revenue because the sites getting the most hits (and thus referrals to the adserver) get more money (it can work in other ways too).
Blocking *all* traffic from the listed domains, to the PC, is how they work. Adblock extension in firefox you can add any path, or server, to the list. You could add cableforum.co.uk/* to the list, not that anyone of course would want to! Adblock would know no differently and still say it was an adserver, if you have told it to.
Kerio's ad-blocking will do exactly the same thing though i use Kerio free so I don't know, and can't find out.
BTW Google ads are
http://pagead(x).googlesyndication.com/* block that in Adblock and wave bye bye to google ads (x is a number).