Do Podcasts Justify the Lecture Method of Teaching?

I just read this article in an Edu-blog (blogs where educators ponder the appropriate use of cutting-edge technology in the classroom). In the Maclean's article we read about lectures, nothing was mentioned about the use of podcasting as an alternative. A number of universities in the States now issue i-pods to students and students are required to listen to certain lectures, but they do not need to come to class to do this. They can listen to the lecture while walking to other classes, while riding their bike, exercising in the gym...there are many possibilities. I think there is an interesting element to this (I would guess that a student's attention span would last longer while exercising than while sitting passively on an uncomfortable chair), but the danger is that if this becomes the norm, students will no longer feel they can go for a walk, or a bike ride, or a gym workout without "studying" at the same time. What do you think?