According to WaPo's move to HTTPS blog post:

>Ask any developer at a major media organization what the biggest hurdle to HTTPS adoption is, and the answer is always going to be advertising. However, unless you understand the ins-and-outs of how digital advertising is implemented, it’s difficult to see why this presents a challenge.

from https://developer.washingtonpost.com/pb/blog/post/2015/12/10...