IOF, my heart goes out to you. You are so close to your birth, your head must be crazy right now. Good luck, I hope everything goes the way it is suppose to for you.
As far as your original post, I think you are right to wonder, I have thought the same myself. My guess is that it comes back to liability. If you rupture during pregnancy or 'false' labor (an event which I have seen documented in studies but I don't know where I saw it anymore) it is just one of those things. If you rupture during labor, then the OB/midwife/nurse/hospital has responsibility and lots of questions come up about monitoring, predictability, saving lives etc. At least that is the way I see it playing out.
I think you are also correct, that the length and intensity of contrations makes a difference. I have seen studies on the ICAN site that show that prolonged ACTIVE labor increases the risk of rupture, and my midwives say that this is part of the thinking behind the 'trial of labor' theory. For example, when I go for a VBAC in May, I will not be allowed to stay at 6 centimeters for 6 hours without serious monitoring and discussion of surgery. And since the studies show that the rupture rate doubles or triples during prolonged active labor, and my risk is increased since this is my fourth attempt at a vaginal birth, that is just fine with me.