I haven't seen the show yet but from everything I've read about it they're using a "button ante" structure. Rather than have everyone put in a $100 ante every hand they have the button pay the ante for everyone before the start of the hand.
So at a six-handed table the small blind puts in $200, the big blind puts in $400 and the button puts in $600. Note that the button's $600 in antes is dead money - it doesn't count towards his calling or raising, it just goes dead straight into the pot.
No idea why they've chosen to do it this way, possibly because it'll speed things up a little and ensure there's no arguments over exactly who has and hasn't anted.