Google is showing a more descriptive search snippet for when it cannot show any search snippet in the search results.
If a page is being blocked by the robots.txt file, Google won't show the search snippet (description) in the search results. Google may show the page in the search results because of the linkage data it has. The example in the picture above is the only URL I have blocked from Google indexing it. I regret writing it, but also would regret removing it, so I blocked it from Google.
If you try to match on it within Google, it turns the notification:
A description for this result is not available because of this site's robots.txt – learn more.
The learn more link goes to the page named Block or remove pages using a robots.txt file in Google's help section.
I think this provides a much better search experience for someone who sees these blocked pages.
I do wonder if they show up for non site: command searches, I'd assume so.
Forum discussion at WebmasterWorld.