Not in close proximity to the Deaf community myself, but my understanding is that “Deaf” is capitalized because it refers not solely to the condition of impaired hearing but also to an entire culture that connects this community. By (potentially controversial) analogy, this is why you sometimes see Black capitalized but not white, within the same publication – in the US there’s generally considered to be a somewhat cohesive Black community, but there’s no single community of whiteness (even though it does represent, in broad strokes, the dominant culture).
Additional background: http://www.deafcounseling.com/whats-up-with-the-big-d-in-deaf/
