Yes, that`s exactly the point I was trying to make, any great difference in the two dimensions will cause the front wheel aligment (toe-in/toe-out) to vary with vertical suspension movement. Also, in the case of body roll one wheel will be pushed in one direction and the other the opposite way, which is not quite what the designer intended, and won`t do much for stability.
In an ideal world, the the two dimensions would be the same, but there is obviously some compromise involved as the ride height varies at any given time, affecting the vertical angle of the track rods and thus the wheel geometry.
The problem is to minimise the effects.

Colin.