Nekusar and the new damage redirection to planeswalkers
Correct. 

Most cards that previously dealt damage to a player received errata to allow them to target a player or planeswalker, but as Nekusar’s ability is not targeted; the standard errata wouldn’t have made as much sense (mostly because you don’t choose or target a player).

You can see the current wording of any card in Gatherer; the wording there is what counts. And with the planeswalker damage redirection rule change; the question is simple for any card; because cards that can damage planeswalkers will specifically say so (or they will say "any target").