Ed,
Driveway is right. You remove the top of the rootstock later on.
Every grafting technique has a reason for existing. Some techniques are suitable to more than one application, and some are very specific. One of the benefits of chip budding or T-budding is the minimal use of scion, e.g. one bud. Wedge, whip, and whip and tongue, for example, generally use more scion (more buds) per graft, and thus produce fewer trees per unit of scion. When T-budding a citrus, for example, you need the top growth of the rootstock to provide energy and nutrition to the plant while your graft is healing in and getting started.
Is it the best method for figs? Don't know, but this was done as a proof of concept, so that people who have situations where it might be appropriate or useful would know that it works, and how to do it. I did some wedge grafts, at the same time.
If someone were to discover a nematode resistant fig variety, grafting of figs would almost instantly become a widely used technique, for example.