It's not actually an "old" style, it's really a new style. Wheelie bars of old were ment to reduce wheelstands, keep the front end down, and that's about it. Then for a stretch in the mid-late 90's, some floppers didn't have wheelie bars at all. Then they went to a single, then an adjustable single wheel as a way to get a target wheel speed at launch. The double wheelie bar now is fully adjusable on each side it looks like, and has worked pretty well. As we were told the purpose was to keep the right rear tire from squatting more then the right.
Dale Armstrong had kind of a similar idea back in the early 90's when he ran a "training wheel" off the side of KB's car right behind the motor that stuck out a couple feet, and would roll on the ground when the chassis flexed on launch, to keep the chassis more straight and not plant that right rear so hard. If I remember right, the car that went 300 had this device on it.