Tadoku has got to be known quite widely among English teachers, students and grown-ups who're made to take a test such as TOEIC out of the blue at work in Japan, and some people, not many of course but, are aiming to read up to one hundred million words! by now. Hey, I'm not kidding here, 一億ですよ、はい。Some tadokers are madly into tadoku and have nil idea to go back to the old habit of studying English. You'll be surprised to see how happy they can be when they got together and talk about their tadoku experiences like kids.
On the other hand, it's resentful but apparent that some tadokers don't seem to find anything amazing with their tadoku reading once they've reached one million words. Some decide to resume English study and try to aim at a higher score with TOEIC or even be allured into other strange methods, sad to say.
Why do you think those completely opposite attitudes are nourished when they do the same tadoku?
There should exist several reasons and I think one of which might be that if they're interested in using English besides reading or not.
Those who have a clear idea that they do tadoku because they want to be a good and fluent user of English and output, speak/write, English some day would naturally change the way of reading books as their purposes require, I assume.
Sometimes they read books for sheer amusement and enjoy being involved in a story wholeheartedly and won't get fussy about the usage of English at all. They don't mind skipping some parts they are not so sure as long as they can feel the story to their heart's content. Other times, learning English usage itself will be their priority than enjoying the story, so they'd read books slowly and analytically and try to learn how English grammar works.
Then what if you're not into using English other than reading books? Do you think you're going to start to take such a tactful reading technique voluntarily? I don't think you can be aware enough what you should be learning while you read books. No matter how many books you read, what you acquire during the reading unconsciously might end up being relatively slim.
I believe strong drive to become a good user of English and use English as a tool to get to know people all across the world through speaking and writing English is the key to be a competent tadokers.