This paragraph sounds like modernist self-back-patting, to be honest. Several things:
* Newton lived at the same time as Boyle, the man often considered to be the founder of scientific chemistry. Newton and Boyle both contributed to the scientific method, and while Newton may have been an alchemist, at the time, the very concept of pseudoscience was still being worked out. Newton's alchemical formulae are not useless; we've replicated "The Net" [0], one of his recipes. The idea that one must "sort out chemistry from alchemy" betrays a total unawareness of the history of chemistry.
* The concept that technology and magic are different was not yet invented in the time of Newton. Newton's research was in natural philosophy [1], the field which predates modern science. He was interested in how the world works, and unlike today, he did not have a roadmap showing how the different fields of study interrelate. Asimov's saying only makes sense in the context of modern science, wherein we (think that we) have enough of an understanding of the world to be able to claim that any magic which we do not understand is merely technology which we have not yet discovered. It's a pretty bold claim, and may be right, but it is based in a (literally) non-Newtonian worldview.
* Compare and contrast Newton with a modern 5-year-old. How much science do you think that the child needs in order to comprehend a phone? (Ask any parent for the answer.)