The majority of journals I know provide an open-access option: you pay a few thousand dollars publication fee such that everyone else in the world can read the electronic version for free. PNAS has this option. Nature, I believe, make an article free in several months/a year if you opt to open access. A few funding bodies, such as Wellcome Trust, have requested to publish in the open access model for several years (these funding bodies pay for the publication fee as long as you can get your paper accepted). I am not sure what the Gates foundation is doing differently here.