Although it may no longer be true in two years, it is relatively safe to say that at this point in the evolution of commercial CAD, one can make a simple distinction between the desktop and the turnkey systems. Desktop systems are drafting systems, generally purchased by users whose needs are local, well-defined and practical, and whose requirement of that system is principally as an aid in the creation of drawings or other visual artifacts such as renderings. The turnkey systems, on the other hand, are intended by their creators to build complete digital representations of real-world objects. This is called a model.
It is important to understand that, even if levels of technology were even closer than they now are, this would continue to be a fundamental difference between the two. Take away the integrated applications of a turnkey system, and you would be left with a system whose purpose, at least from the point of view of those who produced it, was to provide high-level modeling capability, that functionality having been developed to address the most difficult problems of manufacturing companies, not merely to provide a basic design solution; and certainly not as a system for simply putting lines on paper.
Since the turnkey vendors believe themselves to be in the business of providing modeling capability to be accessed by the world of applications, they universally tend to regard drafting and drawing production as a necessary, but technically unchallenging, therefore unimportant, adjunct capability. I mean, anybody can create a drafting system, can't they? Where's the challenge in that?
The challenge was not technical, of course, but financial, and Autodesk saw this early. Its customers, who are much different from turnkey customers, made it successful and are continuing to do so.