The story must encompass all possible player actions and motivations!

He seemingly hasn't heard about terms like "railroading" and others from pen & paper roleplaying theory.

Because "railroading" ist the direct opposite to that. To this "… must encompass all players' actions and motivations".

My personal prime example to railroading are Blizzard's action-RPGs. No choice, a funnelled pathway, the story progresses in exactly ONE direction … ven the character stats are outlines so NO other possibility of solving quests is even ALLOWED … Social interaction ? No way !

There are several theories of how role-playing could be performed, which mechanisms support that or distract from that … One, for example is that of "player empowerment". A mechenism (ora set of it) which enables players to change the story. An example would be that in a round of players every player gets the chance to be the game master for a certain amount of time.
And of course this isn't viable on the PC.