They are established article pages, but my site is under 110 pages and I am always making tweaks. For instance, about a month ago, I discovered and removed some dead links on those pages. Google has yet to deep spider and recache. Beyond things like that, how often should an article page change? I can understand a news site or blog getting hit frequently because of new content that hits the homepage, but on the permanent url for an article (on a news site or a blog), it doesn't seem that the content would change any more/less than mine. Those articles/posts become an established part of the site.
By the way, I am just making an observation, I don't mean to give the impression of whining. In general, I think it's interesting that many of us have seen something similar since mid January, and I assume they are focused on Caffeine.