Speaking as a former reddit admin who had direct access to the server logs (and "wc -l"): Quantcast (and Alexa, and Comscore, and all the others) are terrible at estimating traffic. They make wildly inaccurate guesses using low-quality source data and all the ad execs just gobble up their results as if they're fresh off God's own LaserJet. It's very frustrating to watch. The most accurate results are visible at Googl…
Heck, they didn't even bother to read the numbers reddit actually publishes.