You might be right about the overall move toward giving away music, but in this case, it's because they simply cannot get their music released digitally due to

You might be right about the overall move toward giving away music, but in this case, it's because they simply cannot get their music released digitally due to rights/sampling issues. Giving it away sidesteps the issue, gives them much more exposure, generates a lot of goodwill toward them and will get more people to come out and see them when they put on a concert in your area.