You'll find that the majority buying it weren't even born or old enough to have any idea what politics was. You would have to be at a stretch at least 40 years old, and how many 40+ use the likes of ITunes compared with less than 40? 17 and under use ITunes twice as much as all other age groups.
Plus it doesn't take many sales to get to No.1 otherwise Bieber wouldn't be known
