I am glad the wagon is making a come back, and while I do think that it will replace the SUV for some people (mainly the people that want or need better gas mileage) I agree that they will probably pull more people away from minivans than any other group.
As far as why trucks are not being "targeted" as well, IMO that is because both SUV's and wagons are primarily built to be people haulers. Sure they can haul stuff too, and SUV's can tow stuff as well, but they are built to haul people. Trucks are usually built to haul stuff (there are exceptions), stuff that often times would be difficult or completely impossible to fit into a SUV or to a greater extent wagon.
My parents have an 1996 Suburban that is primarily used to haul the family on trips (it was that or a cargo van, there are 9 kids in my family). Every time I have needed to use it for something beyond that, like hauling an engine and/or transmission or even just wood, I have to take seats out and put them somewhere and then take special precautions because of the carpeting in the "cargo" area. It is really hard to hoist an engine on an engine stand in and out of the back of a '96 Suburban (I am not sure about other SUVs) and would have been impossible with a wagon. It would have been a lot easier with a truck. Atleast that is why SUVs and trucks are not clumped together in this case.
David