Some subjects have more lucrative ads than others. For instance a hub about life insurance will have higher value ads on it than one on, say, your favorite tv show. You need a full breakdown of views for each hub to get an understanding of the figures. You can have lots of visitors to your tv show hub and earn less than you would with a lower amount of visitors to your insurance hub.
Also, clicks are taken into account, so you could have a higher amount of visitors but no clicks.
The asterix is explained on earnings page.