If you compare the UK timeline with the US timeline, you may notice a rather obvious difference. The US page will very often have the President in the first place as the most frequent piece of language in a given week, while the UK Prime Minister will often be hidden behind several other issues of the day.
So what's up? Are Obama's spin-doctors better than Cameron's, meaning that the background chatter of politics talks about him a lot more? Or has the USA got something the UK hasn't when it comes to its leader?
The answer is a little simpler than either of those options, and the key is in the name of the country. The United States. The UK in its entirety is small enough to fit in most American states, and its regional chatter is much closer to its centre. The USA by comparison has fifty separate theatres of regional chatter, and among the few things that you'll find them all talking about is their President. So when a language technologist aggregates all the chatter, he naturally floats to the top.