We're used to thinking of open access as primarily an STM phenomenon: science, technology, and medicine. It makes sense, since researchers in this area seem to be more likely to embrace new channels of information dissemination, and new research in these fields can be so expensive to access; one of the principles behind the open access movement is to make published scholarship accessible to researchers who lack the financial resources to gain access to expensive scholarly publications.
The humanities, in contrast, are seen as still relying primarily on print, which in general I've found to be the case (JSTOR being a notable exception for many faculty).
Today, though, Inside Higher Ed reports on Open Humanities Press, a large new hat in the open access ring and notable precisely because it is dedicated to humanities scholarship, not STM. Even I've heard of some of the names on the advisory board, and with the exception of music, I don't spend much time with humanities literature.
There's been much discussion in librarianship as to if and when the humanities would jump on the e-scholarship and open access bandwagons (not the same things, not by a long shot, but they're in the same parade). This looks like it could be a significant step in that direction.