The points you bring up in #129 are quite valid IMHO, and this is a reason why I do not make a "7 week" distinction. The logic of my position is this:
sentience is the descriptive factor that distinguishes between what it means to be a human
being - a person - and a conglomeration of human tissue with the potential of creating a human. In order for this to happen, one needs a brain. The development of the brain and other structures begins at week three. So I can say before week three there is no brain development, therefore not a person. However, after this development begins, I cannot point to a spot where the embryo for the first time, in fact, becomes sentient and therefore a person subject to rights and priviledges granted to all humans. For these reasons you can see why I do not support abortion, but have no problem with cloning of pre-differentiated cells.
It's a bit of a different take on the whole "abortion/cloning" issue, and I cannot find a friend in either camp. I seem to upset everyone involved.
I would distinguish between having central nervous system tissue and having functional higher brain regions. When a baby is born it has less functional higher brain than a dog. This develops pretty quickly, but you aren't born with it and doesn't start bootstrapping until after birth.