I personally know multiple, sad people who maintain 10+ fake facebook acoounts in order to create fake images of themselves. I can easily imagine really high rates of those people in such a network. Especially if there is nobody trying to avoid this kind of accounts.
I don't know if there is any benefit you could get by having many accounts, but if there is, I'm really sure it is used a lot.
I know a lot of people that have multiple Facebook accounts, some are kids that want to push different updates to different people for example, or a "games" account.
Others are men with a "dating" account and a "family" account.
I guess the same happens in Badoo. Also, they must have a lot of dead accounts and count them (much like Microsoft does).
Their numbers do seem inflated, I don't know how much (50%? 100%?). I'm their active users must be at least an order of magnitude lower (my own account is inactive at the moment).
I don't know if there is any benefit you could get by having many accounts, but if there is, I'm really sure it is used a lot.