The problem is that "the laws of physics" is a phrase that means two different things:
(1) Rules like Newton's laws.
(2) What the world does.

Rules of grammar are formal rules like (1) and not about (2). You can use statistics to see whether (1) matches (2) but there's a lot that can be said with math about formal rules. You can use math to show that two kind of theories are equivalent or that they are different.

There's a lot about the rules of mathematics that you can't learn via statistics. You can't prove NP=/=P by looking at a bunch of examples and using statistics.

Chomsky invented the Chomsky hierachy and from what I remember from my classes at university there's no statistics involved in that way of thinking about grammar. It's still a model of grammar important enough to be taught in computer science classes.