As someone with a small presence in all three overlapping spheres here--writer, reader and listener--I can say that

a) I wouldn't mind someone podficcing my work with or without permission, though I imagine it would be nice to be asked

b)permission isn't a criterion I use in choosing which fic to listen to

c) I do ask and get author permission before recording something because I think it's a nice thing to do and I like the somewhat collaborative feeling of being able to consult with the author about (for instance) musical element.