I wonder how many of those were for medical reasons, where the child wouldn't have survived anyway, or where giving birth would've killed the mother (or both, for that matter). Still, with a percentage like that, it's likely that even discounting such cases, the impact would not be insignificant. Also, since abortion is still illegal in some places (and certainly was in 2010), there are probably some abortions which were not accounted for. All in all, it's a pretty big difference. Certainly not the primary factor behind demographic problems (widespread contraception, economic concerns and rising life expectancy contribute much more), but not insignificant, either.
Certainly, unwanted children are not a solution to aging nations, wanted children are. However, abortions make it easy for the mother to change her mind halfway through. With abortion fully legal and not stigmatized as much (will happen if issue is definitely decided on and controversy is sidelined), the number could be expected to rise. And it certainly wouldn't do neither the future pensioners nor the treasury any good. While I do support the right to abortion on principle, I have an uneasy feeling about it being exercised irresponsibly.