I do also think that reading is easier to progress in even in the presence of inadequate instruction if the child reads a lot. I've always said that dd12 picks up language arts (reading and writing) by osmosis. She's almost never been taught anything in LA that she doesn't already know yet she's always made great strides in that area b/c she loves to read.
Math isn't something that most kids are exposed to informally throughout the course of just living. Of course it does play a part in a lot of things, but most kids aren't using it just to function. They're not the ones who buy the groceries, figure out how big the box surrounding the swing set needs to be if the slide is 12 feet long and attached to a playhouse that is 10 feet off the ground, etc.
Even with great natural ability, in the absence of some instruction, most kids likely won't make as much progress as they could in math. Unfortunately, some schools will use the lack of amazing math achievement scores as proof that the child doesn't need more accelerated instruction rather than proof that they haven't been instructing the child to his level of ability.
