My older and younger sons are just like yours with respect to reading.
My husband and I read to them both every day when they were young and kept it up well past the point when they could read to themselves; it was an important part of our daily interaction with them. We modeled reading ourselves, reading for pleasure and reading to learn, both. We talk about books all the time, we read aloud together every week, and we both write. Our house is full of books and magazines across a very broad range of subject matter.
The older read his way through a degree in philosophy and a J.D., both with top honors. The younger reads only what’s on a computer screen.
Yet the younger also seemingly absorbed everything he did encounter in textbooks during his several abortive attempts at formal education, and he retains it in detail years later, well integrated into his world-awareness and readily retrievable in conversation.
Both are highly intelligent; the older is clearly a left-hemisphere-dominant type, logical and verbal. I can’t say that the younger is right-dominant, but I can easily say that his right-brain functions are much more pronounced than in the rest of us. He is a Gestalt person, a whole-picture person, who can size something up, see how it works (whether machine, process, or person), and see what would make it work better. I think reading is just too linear, measured, deliberate, and slow for his type of mind. If he wants to know something, he looks it up, reads what he needs to know (and remembers it all), and then goes on his way.
I think reading is part of a natural discipline that belongs to a larger constellation of behaviors or mental faculties and that they can be nurtured but not forced. Much as I hold reading and literature as a value, I would be wrong to try to demand that my younger son adopt it, just as I would be wrong to force him to follow my religion if I had one.
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[Edit] As a postscript, I would have to offer a counterexample to @thorninmud‘s in that my younger son is and always has been the one with the flourishing gardens of imagination—some of them Rappaccini’s gardens, to be sure, but without a doubt dense and rich. So I do not see a correlation between imaginative capacity and readership. Rather, to me it appears to be between mental structure and verbal behavior.