I think that when Zork was first written in 1978 or 1979, it was "inspired" by Dungeons And Dragons and I think for the perspective at the time, the programmers thought that they were making a computer version of the D&D. Recall, that in the 70's and early 80's the "role playing" aspect of RPGs was much stronger than it became in ensuing years. When I first played D&D in 1980, the DM was very much about us staying in character and playing his "story". My feeling is that as computer games rose in popularity, and they could keep stats much more accurately than people with pencils, stats slowly became more important than "role playing". In my later years I recall games like Warhammer and Battletech that were almost all stats. Anyway, I think the guys who wrote Zork did have D&D in mind, but more of the "story"aspect then the stats. If Zork is not an RPG, it was inspired by them.

Zelda on the other hand is simply an action arcade game that had an inventory and a mild story that was compelling because it was one of the first games to meld those elements into a home video game. I have tried to play all the Zelda games and every one has left me cold. However, Final Fantasy I rules (off topic, I know)