Broadly, I see two types of visitors to these kinda sites:
1. Someone new, who's most likely just following a link (like us) - they haven't even had a chance to read the article yet & knows nothing about the site, it's reputation, quality etc. All a pop up does is annoy a new visitor. I highly doubt people will take the time or even trust to give away their email with no obvious benefit.
2. A repeat user, someone who's familiar with the site. What's wrong with placing a simple signup form at the end of the article. It's unobtrusive & if people really like your stuff, they will sign up.
Or is it the case that people like us are not the target audience - they couldn't give two shit*s whether we stay on the page or not. Fortunately I haven't had to deal with SEO and shoving stuff on users to sell my stuff, so perhaps I'm naive.