COMPULSION
...but it will provoke opportunity attacks ...
MAGIC MOUTH
... will trigger the spell ... etc. etc. etc.
Will is used in multiple ways in the "natural language" rules-
Willing / unwilling.
Will (as in willpower).
Will (as in deterministic mechanics).
Again, I agree that it's a weird rule, a throwback rule, and a rule that some people don't like. But the arguments that it isn't a rule are just weird. Bad rules can be bad, or poorly implemented, and still be rules. If it was just fluff, it wouldn't be in the multiclass table as well.