All of them kind of are if you look at it that way. They say if you deposit $50 you get $50 free, they just don't tell you up front that you have to work for it and it gets distributed in small increments.
Its a great business strategy for them. They get people that see the "Free" money and they depsoit, well if they lose that money then they don't have to pay because they haven't met their requirements for the bounus to be distributed.
Also on the same note, your basically getting your money back in theory. I say this because when you play tournaments you get fee's taken out, and when you play cash games, your getting a rake taken out, so that money goes back into your bonus account.