Jeffrey – as other commentators say, reputation is a great motivator. But also, if you already get paid to work as a teacher, and then you create content which you share openly (perhaps video, audio, slideshare, Prezi, etc), then others can use it. If enough do this, there will be rich content available, and there will be a critical point reached which would make this approach seem normal. Some recent initiatives include i-Tunes U and even changes in pedagogy (Flip lessons, course websites, etc) are making this type of content easily searchable and available.
True, publishers are trying to protect their business. But teachers can benefit much more by sharing.