I'm no expert in any field, especially law but....
In the case of your car, common sense would say, no, you wouldn't have a claim if nothing happened but if we make your car example a little closer to the case in question the answer could be different.
Let's say you took your car for a service at a garage and the mechanic failed to report the fault, if negligence on the part of the mechanic can be proved a breach of contract case would seem reasonable. If loss or damage is caused due to such negligence compensation for any such would also seem reasonable.
If you apply this logic to the case of the child that never existed you could argue that a loss has been incurred due directly to the original negligence. However if no option of termination was available the second child would have had no chance to exist regardless of the original negligence, in the article though it seems that the main point was that termination WAS an option, hence the "for being born" statement.
With regard to the parents option on termination, I believe it's not only important I believe it's imperative that the choice remains with the parents, that's why it's important to understand exactly WHY the compensation claim was upheld.
Let's presume for a moment that the court had made the decision that the child should not have been born, how long will it be before Science and the courts extrapolate this retrospective decision and claim rights to the options of birth/termination?
Great subject BTW