that's pretty much it. when we started having (male) doctors deliver babies (when birth became medicalized) they found it easier to see what was going on if the woman was laying on her back. It may be easier for the doc to see but it makes it MUCH harder for the baby and the woman to give birth. Not only does it make your opening narrower, but it works against gravity. Many complications in birth can be avoided by birthing in a more upright position. the article i posted explains the history as well as better positions to birth your baby in.
this is why having the fetal moniter on all the time as well as other interventions during labor make it virtually impossible to birth in other positions. it is why knowing ALL of the consequences in choosing interventions is important.