It's not just that COI is up there with the country's biggest advertisers. After all, being on the roster is no guarantee of a billings windfall. It's what being a COI agency says about the sort of company you really are.
The COI roster has become a thermometer whose needle pinpoints who's hot and who's not. There's no doubt that occasional observers of the ad industry (and that includes many clients) see COI agencies as a cut above; when it comes to who to include on a pitchlist, the ill-informed advertiser will clutch at such straws as evidence of agency quality.
For those agencies unceremoniously kicked out of the club, of course, the implications are painful: couldn't hack it/behind-the-times/didn't deliver. Supply your own crushing reasoning. Whatever the behind-the-scenes truth of the matter, being on the COI roster is still so covetable that a dumped agency finds it hard to brush off the slight. Any claims of "creative differences", "difficult client", "poor payers" or any of the myriad excuses agencies resort to when they lose business just don't wash when it comes to COI.
So the release of the new roster this week tells many stories. WPP comes off badly; its three powerhouses - JWT, Ogilvy & Mather and Grey - have all been dropped. Fallon - a blushing debutante last time round - has also gone, having made no impact whatsoever. Saatchi & Saatchi (the COI chief executive Alan Bishop's alma mater) and Euro RSCG - both agencies that have gone through dramatic changes since the last review - are off, perhaps until they have stabilised their propositions.
The arrival of youngsters VCCP, Wieden & Kennedy, Farm and Clemmow Hornby Inge will add some welcome new blood, and the appearance of the seasoned Bartle Bogle Hegarty only makes you wonder why they weren't there before.
For all that, though, being on the COI roster is a mixed blessing. The positives far outweigh the negatives: COI is a "decent", well-organised client that makes fair and prompt payment, offers great opportunities for creativity and the chance to work on issues of real social importance, and confers invaluable kudos. But the negatives can be a small but difficult price to pay, not least the bureaucracy and the lurking threat of interference from capricious ministers.
There will be some tough questions asked as agencies digest the latest roster rethink. With the advertising economy still faltering and with COI spend now nudging towards £200 million, COI has never been a more covetable client.
There was a time, 30 years ago perhaps, when news of a new chief executive at FCB London would have got the ad industry twitching nervously. Nigel Jones' arrival in the coldseat is likely to have less of an effect.
That's no reflection on Jones himself, a consummate, if low-key, front-man and an established player in the direct marketing arena. But the idea of FCB making any serious inroads into the competitive London agency scene now seem as likely as IPG winning an accountancy award.
FCB's problems have been well documented, but pretty much come down to one key question: why on earth does FCB need to exist? Right now it offers nothing new, different or exciting in the London market. And as a network, it is treading water in the grey middle ground. Steve Blamer, the network's global chief, is widely considered an energetic, capable man - much the same as Jones in London. But until they can offer a real reason for the continued existence of their agency, FCB will continue to be advertising's black hole.