I can't say I agree with all of your examples of good science writers. Hawking, for example, is a terrible science writer unless he's got somebody like Mlodinow to do all the actual writing for him. I've talked to a lot of people who are completely turned off to pop-cosmology books because of A Brief History of Time. Oliver Sacks too, though I absolute love the guy, can be overly convoluted. Hell, the guy has footnotes that literally fill the majority of the page!

You should check out Mary Roach. Her book Stiff is probably one of the best pop-science books I've read.