They also qualified that, "The list may look very NVIDIA heavy, but part of it is that we simply sell more NVIDIA cards than AMD cards, so there are more NVIDIA models that we have sold enough of to be confident in our data." In addition to this fact, even though they sell more NVIDIA cards, the NVIDIA GeForce cards on a whole were much more reliable in 2013 than AMD Radeon cards. NVIDIA GeForce cards only had an overall failure rate of 3.3% versus AMD Radeon cards which had an overall failure rate of 10%. This marked an increase in AMD's GPU failure rate, which is definitely a step back for the company. They also mentioned that Nvidia's professional cards had a failure rate of 2.05% while AMD's had an almost identical 2.17%, which isn't surprising considering that professional cards are fundamentally designed and tested to have lower failure rates.

http://www.brightsideofnews.com/news/2013/12/27/whats-the-most-reliable-hardware-of-2013.aspx
The whole article is a good read and I first thought "Yer, AMD have more failures, as they have sold far more cards than nVidia but not the case. QC failing? I thought 3% was bad but 10% is crazy bad.