Steve and Jerry have both been writing about the idea of podcasting lectures.
I think part of what faculty members don't say when they flinch back from the idea of posting their lectures (as notes, full text, or podcasts) is that they are afraid that their lectures will be revealed to be less polished, less original, less important than their published scholarship.
However, we need to also be careful about dismissing the concerns about people not coming to class (and certainly there are ways to address that). But I've had a number of conversations with students who have told me (confidentially...) that if there were podcasts or lecture notes that they would come to class much less, or not at all, even if they took the hit for class participation. [I might add that some institutions of higher ed discourage or even prohibit professors from requring attendance.]
I would also add that if one runs a truly interactive lecture, then students are missing a great deal by not being there to participate in that process. Like it or not, posted materials suggests that active learning is less important than passive learning (even if the hope is that posting such materials would result in a more active engagement with the material).
I understand the appeal that broadening the podcasting or vidcasting of lecture series to all class lectures might have. But remember, most of those lectures in something like Great Lives required weeks of preparation by those scholars for one 75-minute presentation. The harsh reality is that most class lectures are composed in an hour or two and don't come close to the quality in content, presentation and delivery of a formal lecture.
None of this is to reject the premise of podcasting lectures, but merely to explain that such a process should be undertaken carefully, especially for junior faculty members who have their professional reputations (and future employment) to consider.