Actually, the same argument applies to all the metrics. And while I agree with the performance argument, there is the argument about code readability, maintainability and standardization (implementing a common interface).

I propose:

1.  You add detailed documentation to the methods about what all they are doing.
2.  Sometime in near future, we refactor code in other metrics to use a similar approach (and decide on the approach. E.g., renaming parse() to parse_and_calculate_stats() )