The point I was trying to make with the partial functions was something like “Yeah, there are 0s, yeah it is bad, but at least we can never assign low probability to any event that any of the hypotheses actually cares about.” I guess I could have make that argument more clearly if instead, I just pointed out that any event in the sigma algebra of any of the hypotheses will have probability at least equal to the probability of that hypothesis times the probability of that event in that hypothesis. Thus the 0s (and the 10−9s) are really coming from the fact that (almost) nobody cares about those events.
The point I was trying to make with the partial functions was something like “Yeah, there are 0s, yeah it is bad, but at least we can never assign low probability to any event that any of the hypotheses actually cares about.” I guess I could have make that argument more clearly if instead, I just pointed out that any event in the sigma algebra of any of the hypotheses will have probability at least equal to the probability of that hypothesis times the probability of that event in that hypothesis. Thus the 0s (and the 10−9s) are really coming from the fact that (almost) nobody cares about those events.