
Am I the only one who finds this slightly creepy? He's been in power for less than two years. Obama would be, at the moment, somewhere in the low 500s, and he only gets even that far by simply being the President of the United States at a time when it is still (barely) a hegemonic power, and not because of anything he in particular has done.
My guess is that he's on the cover because he's topical.
There's an entire branch of trade publishing which basically just kicks out books every month based on controversy and the top google searches. They use stock photo and licensed text blurbs to put together books
extremely quickly.
I applied for this job a few months ago at this publishing house which operates like that. It was some significant date relating to Marilyn Monroe, so there were a lot of documentaries on TV about her. They were able to publish a book of marilyn monroe quotes in about three weeks, fast enough so that it was still topical by the time the books hit the shelf. You usually find these things near the register at Barnes & Noble on sale for 50% off.
So my guess is that Brittanica has a publishing office which basically just zips out books in record time by manipulating photo and text assets they already own. If a movie comes out about, I dunno, Martin Luther King Jr, they'll quickly pop out a photo anthology about his life so they can capitalize on the buzz.