In early February 2011, many Blogger blog owners, who tracked blog reader traffic by using Blogger Stats and Google Analytics, were wondering about blog traffic from mysterious sources, like "bit.ly" and "goo.gl". When informed that it was fraudulent activity, and a type of spam, they thought no more of the problem, and moved on.
What these blog owners failed to realise is that while needlessly alarming them about their blogs being under attack, Referer Spam was also artificially inflating the blog activity numbers. Owners of newer and less popular blogs noticed Referer Spam more, as their blogs seemingly had gained popularity overnight, with hundreds or thousands of pageviews daily.
Recently the Referer Spam entries in Stats have been conspicuous in their absence. Like banging your head against a wall, then wondering about the absence of pain when you stop, the latter blog owners are wondering about the apparent sudden drop in blog activity. Whether Google figured out how to filter the fraudulent traffic, or whether the spammers behind the traffic tired of their useless game, the traffic has stopped.
Whatever. If the Stats numbers for your blog have recently dropped, maybe like a stone, you haven't lost readership. You never had the readership in the first place - just noise, not even idle page views. You didn't lose what you never had.