I’ve been noticing a few discrepancies in both indexed pages and the SERPs… There’s either a dance going on, or as you suggested, a big spring clean.
One thing a number of people have noticed, and Jason Duke brought up at CAC in Amsterdam, is the fact that some people are getting different results when they are logged into their google account (be it gmail, analytics, webmaster tools, adsense or whatever) than when they are not! Trying logging out, clearing your cookies and checking your serps/indexed pages again