Including rape in Case 1 makes sense only if you take the position that the sacredness of life would be breached by compelling childbirth after rape. Which is certainly arguable, but then it would be equally arguable that sacredness of life could be breached in other circumstances that don't involve the literal death of the pregnant woman.
The difficulty I have with Case 2 is that it seems to elevate the characteristics of the foetus (ie its viability) over the fact that it IS a foetus, that is, over the fact that its entire existence is inside a woman's body. When to my mind the latter is the whole point of the right to abortion. But you are right, these are very rare cases.