As with the Stargate vs. The Hobbit post before, I realize that these little ads on Facebook are not supposed to be direct comparisons of popularity, but the way they are presented still comes across as quite funny to me.
I’m pretty sure that, in reality, J.K. Rowling is much more popular than Terry Pratchett, but the way Facebook chooses to present these things might make you think otherwise.
I think somebody at Facebook needs some lessons in effective data presentation.
On the other hand, they appear to have humorous juxtaposition well covered.