>>I'm definitely under the impression that it has a whole lot to do with the ratio of thin pages to actual content pages. That Digital Trends site has 34,000 tag pages and 33,000 actual articles indexed.
That may be a factor. If so though, that seems like a flaw in Google's algorithm that it counts legit tag pages as "thin content", unless Google has just suddenly decided no one is allowed to use tags anymore... though it would have been nice if they'd given the world a warning since tags are kind of an internet standard.
Several of the sites we've discussed here have said on the Google Webmaster forum that they disallowed or noindexed all their tag pages, and I don't think that's helped them any yet. So hard to say.