A post on "Approaching Lost" (www.approachinglost.com) brings up another mystery that we surely need to know by the end of the show. That is, why can the Island/Jacob cure diseases (and flaky sperm counts), but not the rancid uteruses and toxic pregnancies? We are led to believe that the Island might somehow actually cause the aging uterus problem, so healing it would not apply in that case anyway. But why doesn't the island create super-babies with its wondrous healing properties while the uteruses are still viable, rather than adversely affecting the fetuses causing monster growths that attack the mother? Which also begs the question, how were the Island natives able to propagate before the DI came along, but that's for another post.
I suppose that we are kind of taking it on assumption that Ben may have ticked off Jacob or the Island in some way, which led to his not being healed of his spinal tumor. Maybe it's because he has not solved the fertility problems yet that Jacob has withheld Ben's healing, therefore letting Ben know that he's moving on to another leader who has the faith to fix the problem (Locke). But then that brings us back to the original question...why can't the fertility problems be healed like Locke's legs, Rose's cancer, etc.?
Is the fertility problem a situation like, a little bit of cure is good for fixing some things, but a large amount can cause problems? For instance, a little medication is good for aches and pains, but too much will wreck your liver. And maybe this contradiction falls somewhere into the area of the blast door map's, "the remedy is worse than the disease" notation? Was Radzinsky really saying that the Island itself may be able to enact miracles of healing in some ways, but in other ways staying on the island is very dangerous and you don't want to do it? As in, it can repair low sperm counts, but stay any longer and it will kill the mother and child? I hope that TPTB will reveal this to us by the finale!