I don't think it is between page views. My site is a one page ajax heavy site, so I can only have analytics on the landing page. The time on page shows around a minute average (changes per day), while the bounces shows nearly 90%. Doesn't fluctuate as much.

Not sure how they do these measurements. But what is really needed is a tool that can measure on ajax sites.

For now i've started counting server side requests, and it really is showing how unreliable Google Analytics is.