"everything the designer adds builds in some sort of genre assumption"

Travis Casey 

.....games with logarithmic ability ratings tend to scale up and down better than those with linear scales, making them suitable for a broader range of genres without major adjustments. As another example, in a skill-based system, adding a single new skill can allow you to support multiple new character types, whereas in a strict class-based system, each new type requires creating another class.
     Thus, while everything the designer adds builds in some sort of genre assumption, a designer can attempt to make choices that restrict the range of genres minimally. Perhaps just as important, the designer can also explain the choices that were made, why they were made, and alternatives... thus creating a 'hacker's guide" for those interested in using the core of the system for other genres. Some games don't attempt this at all, while others make it a major selling point.