The Focus 4 Door has a massive market outside of the UK, it's easier to get into the rear seats than the hatchback and is a saloon, (i know i know, there is an attraction to have a saloon.) It's smaller than the gargantuan mondeo and is a lot cheaper too.
Basically a 4 door saloon. Only, the hatchback is more popular here. You may go ahead and ask why there is a 4 door Fiesta in other markets......i dont know the answer to that.
I noticed a similar trend while I was living in South Africa. Whereas over here small families would tend to have a hatchback Focus, Astra etc or something bigger like a Mondeo, Vectra and so on, over there there was a big market for saloon versions of the Polo, Corsa, Astra etc.