EDIT: Doh! It appears I missed what blutfink was trying to say and that their changing of quantities from energy to power was intentional. Sorry for the confusion.
Whenever you have an energy use figure over a specific period, it is perfectly legitimate to calculate the average power, just as if it took you 30 min to reach your grandmother's house, which is 60 miles away, then you averaged 120 mph. In this case, an average power is an appropriate measure, as we do not know how long this page will be in service.