Learning Sciences: In the learning sciences researchers are concerned with understanding what happens within the learner so that they can explain it and describe the way in which learning occurs. So, although they may design learning environments or learning systems, they do so with the hope that it will be a means to the end of understanding the learning process more deeply so as to confirm a theory or develop a new way of understanding the way in which learning occurs.
Instructional Technology: People in IT do not necessarily disregard learning theory or work that has been done that helps describe the process of learning; however, their ultimate objective is to design learning systems or products that result in learning. So, they do research, investigate theory, and even describe learning. But, at the end of the day they want to see improved performance or improved learning, not just a new theory or a new way of understanding how learning might occur.
While there will probably always be a divide between folks in these two groups, it would be nice if they talked to each other a little more often and recognized that they can collaborate in ways that will help both groups reach their objectives. For the two to live in "parallel universes" (as Edelson describes it) seems quite silly and childish to me.