RE: "Does our understanding of who is a "person" arise from moral considerations?"

No; it is, or at least could be, based upon the point in fetal development where the entity becomes capable of sustaining life without direct support from the mother's body.

My underlying thought was that at some point, a social/legal compromise will be reached that only permits elective abortions up to a certain stage of fetal development. I suspect that early term abortions will be permitted as a matter of personal choice and late term abortions will be prohibited unless the continued pregnancy poses an obvious threat to the physical health of the pregnant female. Nobody would be completely satisfied, but it would work.

If Jon is right, that would support my contention. Abortion is legal now, no? The clauses are just two more reasons why it would remain legal in most areas of the country post Roe v. Wade.