Yeah, why do some animals have their eyes on the side of their heads instead of in front??
I think questions like these are surely indications of ability to think about things in great depth.
My dd4 has not been 'reading' either but she has tested in the gifted range (in effort to apply for kindergarten) and shows other signs of a drive to learn. I have to do a lot of reading out loud what she calls 'information books'. She doesn't always show off her learning, but I think there is a lot getting absorbed.
Reading early is a great sign of gt-ness, but not reading early doesn't preclude giftedness.
