I gave this argument differents thoughts, not only having different accounts violates Facebook's TOS but Zuckerberg states it is "immoral" to have more than one account so people should be ashamed of it. I can understand his position, he has to enforce the fact that every active user on Facebook is a real user.

Now, let's rule out developers that until lately were forced into this behaviour, there's plenty of people out there using multiple accounts. Plenty of people using multiple accounts on daily basis. For example people running businesses/marketing with their account instead of page and much more importantly you know who's using more than one account? Casual gamers, those who play games on daily basis. Every Zynga game (just to point out the most successful ones) is a spam factory forcing users to spam in order to advance in their games, users are aware of this and start their "gaming" accounts. If you didn't think about this yet, just try and check how many people descend from the "Games" family (and that's only for english speaking countries) these days, impressive growth. Now check the "Cityville", the "Farm*" family and so on.

And there's plenty of other categories.

Once I read that Madrid had two times as many accounts on Facebook as the real city population. Now you could point out we don't know how many of this users are counted as active, of course Facebook will never point out the number and will always defend its strenght, but that's something people should think about.