Daring in this company, Andreas Gregersen applies his paper to the discussion of Ludology in relation to Narratology and Semiology. In his understanding ludology is about rules, and ludology is rules all the way down.
First, I think he (and Zimmerman and Salen in his quote) is forgetting another limiting aspect of games, which is the arena. While code is interpreted as law in some contexts, here code is interpreted as rule, but rules the players can not consent to.
If we compare this to playing fields, that means that the field itself is "rule". In the Huizinga definition of play, the field is considered the arena. Certain rules state how the arena is to be: how long, how large goals, etc, but still as all players of games know, one arena is not the same as the other. Physical laws which the game rules can not adjust influences the arena - as for instance when they golf on the ice on Svalbard, carrying a rifle with the clubs, or there are ski-jumping competition on different snow simulations. So what is the rule and what is the arena in computer games?