Contraception and abortifacients have existed for millennia.
People in the developed world are choosing not have children because of costs. Having children in the developing world is an investment that is paid back in the form of free labor, dowries and someone to care for you when you're elderly.
Yes, but not reliably (for contraception) or safely (for abortifacients), and by their nature, 80% reliable contraception is of dubious utility.
You realise the quoted reliability rates are per year, not per act? For example, the withdrawal method (available to everyone, for all time) has a reliability rate of 78% for typical use and 96% for perfect use.  Obviously, even at 78% reliability over a year, that is of a great deal of utility. 78% of the time a woman whose partner practises withdrawal will not get pregnant over the course of a year.
I suppose it could conceivably just be the ability to treat STDs, but I don't think that's enough, personally. YMMV. (Plus I'm not sure that the time works out correctly.)