As a biologist, I would say that you leave out a big part of why popular biological writing is seen as so much richer: biology is a damn sight easier to understand than physics.

I can take almost anyone and given a shortish conversation explain to them the very basics of what I study. Researchers in physics simply cannot do the same, most of the time. Physics is explained in the language of mathematics, and most of us, even the generally scientifically literate, simply don't know enough of this language for physics to make very much sense. Astrophysics is the only area of physics that has partially escaped this curse, because they can sometimes talk about concrete stars, galaxies, planets etc. Even an average biologist can explain basic biology, and a decent one can make it interesting, but it takes a Neil DeGrasse Tyson to explain physics in a way that is comprehensible and interesting.

@1 true story. Charles' idea of beautiful writing excludes the more opaque beauty of mathematical expressions.