Discussion of rape/incest muddies the water for the other 99% and slows progress. That is a possible rationale for your suspicion, wagglebee, although I'm inclined to give jumpstart the benefit of the doubt.
There are nearly 1.5 MILLION abortions performed in the US each year, I would seriously question if even 1% of those are a result of rape or incest. However, I agree with the premise that the pro-death crowd uses rape and incest as a "red herring" to avoid the real issue and that is that we have lost nearly 50 million people in the past 33 years. When you consider that statistically about half of them would have been female and many of them would now have children of their own, the loss is staggering.