Is "Player" interchangeable with "Planeswalker"?
No, a planeswalker cannot be targeted by a card unless explicitly stated; however, they can be damaged by cards that target players.

This is called the Planeswalker redirection rule:


  306.7. If noncombat damage would be dealt to a player by a source controlled by an opponent, that opponent may have that source deal that damage to a planeswalker the first player controls instead. This is a redirection effect (see rule 614.9) and is subject to the normal rules for ordering replacement effects (see rule 616). The opponent chooses whether to redirect the damage as the redirection effect is applied.


So, anything that can damage a player has been pseudo-errata'd to be able to damage a planeswalker.