First thing is Hubpage page view counting method and google page impression counting methods are different. As a result both are not equal. It is one reason, if you see 100 hubpage views, you would see 80 adsense page impressions. This is not an accurate figure but it is not equ, just an example.
Secondly your google ads show only 60% of the time. As a results if you have 1000 hubpage views, only 600 times google ads display in your hubs.