I'm no expert in this subject, but since there are several sources that can cause condensation in the tent there is no easy answer.
Sometimes you think that in the area you're going to there will be no condensation and then you get a lot of it and the other way around.
Except for location and weather there are things you can affect that creates condensation in your tent.
When water vaporizes in the air and then hit the cold fabric of the tent you get condensation. It comes from air, yourself and the ground.
To get less condensation you should use a fabric in the tent that breathes, you should ventilate and you can cover the ground.
So why does it condensate more in an single wall tent? As I said, I'm no expert, but the double wall tents have a floor, so you get less condensation from the ground. If you have a large vestibule, you can cover that ground as well to lessen the moisture build up. They also have an inner tent that breathes a lot. The inner tent fabric is also warmer so that helps against condensation as well. You do need to have good ventilation in a double wall tent. I can also guess that it has something to do with a thermos effect using double wall tents.
To get less condensation in a single wall, you can use a floor, ventilate and carefully choose which fabric to use.
So the difference between single and double wall shoulb be that the double wall have a floor to stop some of the moisture build up, it has a inner tent that breathes a lot and it creates some kind of micro climate that prevents some of the condensation.
It would be nice if someone could do an experiment if you live in a warm humid area.
You know when you bring out a cold beer from the fridge and nothing special happens. The next day or week you do the same and the condensation on the beer can is massive (that kind of simulate warm humid air in a tent hitting a cold tent fabric). I would like to try to pour it in a thermos cup to see how much difference it makes. I don't know if that's a way to simulate a double wall tent though...

but it will taste good! I will probably have to wait a few moths before I can do that here.
One thing you can notice is that if you are outside the house and the wind is blowing, you get a lot less condensation (simulating ventilation in a tent), compared to is the wind is still.
Sorry about the long speculating post...
