As I mentioned in the TC comments, in the context of that list, ‘top’ means most frequently quoted on TechMeme. At NewsCred (my startup), we’re collecting metrics so that we can determine lists of the top news sources as well as top journalists (both mainstream/bloggers), but using credibility as our criterion. We want to highlight writers and sources based on quality, rather than popularity or frequency of posts.
We just launched our Alpha, so the dataset is very limited, but in terms of sources, the Economist and Techcrunch (go figure!) came out on top this week.
Also, the lists will be syndicated each week of course!