Number of pages indexed dropped like a rock

why?

[Compworld]

For some reason, I checked the number of indexed pages from Google on one of my sites, and it is about a tenth of what it was for the last 7 years. The only advertising I do for this site is via affiliate programs (our own), PPC, and other online media. Anyone knows what may have happend?

[longen]

Is the page count more accurate than before - many seo's report google has indexed 10x the actual number of real pages, so they would consider a drop to 10% a benefit.

[Compworld]

Much more than a 10% drop. Like a 60% drop.