That's what I've always understood as well. I'm sure you could use the older style hydraulic/electric brake controllers on a truck with rear wheel ABS only though by splicing into the front brake circuit.If I understand keerucktly, Modern ABS put the Kaibosh on those.
I've always heard the hydraulic/electric controllers work very well and are nice and proportionate. I'd really like to hear what some of the people who have used both have to say about them. I've got one sitting here that came out of an old truck I had, maybe if there are enough good reviews I'll have to install it and try it out.