Except every ISP that isn't a mobile operator or a major UK wireline ISP (e.g. BT/TalkTalk/Sky/Virgin). Including Andrews and Arnold, but also including many smaller ISPs like Zen or IDnet or Xilo and others.
A&A have played a massive blinder on the media front, by saying that they aren't doing something that no one is legally requiring them to do (it would be interesting to see what they do if they were actually forced to, though). It's also worth pointing out that the mobile networks have had filters for years, because of Labour government pressure and not because of the "wall of Cameron" or whatever people are calling it.
I also like how the site says "checked on the main UK ISPs" and then includes A&A, which no one would ever say is a "main UK ISP". They're the nichest of the niche. They're an extremely good ISP (although you can get similar quality from others at a fraction of the price), but they're not a "main ISP".
I would guess that A&A have paid towards the ORG or are contributing something and that's why they're getting prominence.
Or if you're on any of the ISPs who do not have filters, including but not limited to A&A.