I agree, teenagers are teenagers, and these things not only happen, but should be expected to happen. But acknowledging this brings up the very reason that this is a political problem for Gov. Palin.
It might not be an issue at all, except that it appears that Palin has, in her capacity as a public figure, made public statements that she believes "abstinence-only" sex education should be the only public policy. She can't expect that nobody will connect her political stance with what certainly comes across as a conspicuous argument against it.
But once that's said, it's said. I hope that that is where it ends, though I suspect it won't be.
edited to add: by the way, I don't think there's any real evidence that Palin's daughter did not receive sex education, including aspects of it that her mother has stated she would not support, and that is one reason I think the argument should not go too far. For all I know she may have had condoms in her pocket and decided not to use them. I think that anti-Palin forces might well shoot themselves in the foot here. The situation seems to me to drive home the point that because teenagers will tend to be sexually active, abstinence-only education falls short. But it says nothing, really, about Palin's parenting or her personal life, or her family, that this object lesson happens to be so close to home.