It's also not always ideal when research faculty aren't trained to teach and/or aren't interested in getting better at teaching.  Just because UO peer institutions have tenure faculty teaching everything doesn't mean it's the right thing to do.  I've seen some of the instruction at those peer universities and it's not always ideal.  When it works like you suggest that's great, but non-tenured professors can share current research and excite students just as well as tenured, and are often more motivated for, have more time for, and are more trained in effective teaching practices.