[blumkvist]

Some publishers chose to put Quantcast's tracking pixel on their websites. These are annotated as as "directly measured". Vox Media is one of those publishers. If you don't chose to share your data with Quantcast, they measure it through toolbars and 3rd party data, so it's only a bad estimation.

[_up]

Around 25-30% block Ads and probably also tracking pixel, in the US and Europe . I suspect the numbers are probably twice that high on tech news sites. So this alone could probably explain the low estimates.