Digging deeper, this goes to the publisher's own brand; whether it is interested in brand ads or performance ads, whether it sees the future as higher CPM's for fewer ads, or whether it wants to sell out its entire inventory, even as remnant.
For premium publishers, a scarcity of inventory is not only acceptable, in some sense it's desirable. If they run out of inventory, they raise the price, and they actually accept fewer ads. In this sense, they're like old-time glossy magazines; you can only afford them if you are someone they want in the book. Today, as I write, there is only one ad on the entire Huffington Post home page. These are the basic supply and demand principles: scarce supply drives up price.
Premium publishers are also moving quickly toward video. The single ad on today's Economist home page is a video.
And the single ad at the top of the page on Vogue is a rotator with three promos for the magazine and only one slide for the single advertiser on the home page, J.Crew.
For these new formats, premium publishers enjoy high CPMs, which is why they've "sacrificed" clutter. In point of fact, they're responding to readers, who will tolerate an ad or two, but not too many. And those ads are not performance ads -- they're brand ads that associate like brands (the publisher and the advertiser) with each other.
In my ASU class on the business and future of journalism, I polled my students on what they would like to see in advertising support for online publishers. Since they're the Millennials, they have strong preferences, and they want fewer, more interesting and relevant ads. In other words, they'll happily tolerate ads with good creative. I showed them ZEDO's new InviewSlider, and they actually thought it was cool!
On the other hand, non-premium publishers are still insisting on 100% fill rates. They will tolerate more ads, sold at lower CPM's. In general, they don't sell video, or any of the new high impact formats we are now introducing to such enthusiasm. And they are not looking for brand ads -- they're looking for ads that justify their rates.
We believe that the premium brands are what will keep digital media alive, and that advertisers want brand-safe placements that will help, not hurt their brands, and they're willing to pay for that.