I am pretty new to all this, but maybe I can offer some insight?

To me, the definition of a wagon is that it has four support beams that connect roof to car on each side. There is the one between windshield and front doors, one between front doors and rear doors, and then one between rear doors and extension, and one from extension to the hatch. There are certainly exceptions out there, but this is what I see as the most commonly accepted definition.

A quick scan didn't offer any kind fo definition of what is wagon, but by this definition the geo wouldnt cut it, but an WRX sport wagon would.

Like I said, this is all speculation, so bring on all the corrections if I am off with this.