I've only just seen this thread, so your tactics worked a little, Bear!
As far as I reckon, when you are running on uneven surfaces, your feet are going to be pronating in both directions constantly, and moving about all over the place, because of the unevenness of the terrain. This would affect neutral runners and pronators in a similar way, no matter what amount of pronation support you have in the shoes you are using. (I think that this is the reason why it is hard to find a offroad shoe with any support against over-pronation - because there is no need for it in a purely off road shoe?).
So in theory, it isn't as important to wear your orthotics in x-country shoes. Having said that, I am certainly no biomechanics expert and it would be a good idea to check with whoever gave you your orthotics before you ditch them!