A dirty little secret in the CMS industry is that, while in-context editing is often what sells a CMS, the "power user" interface is usually what winds up getting used after implementation. This phenomenon obviously creates problems in the selection process because, when the sales demo focus on an interface that users will quickly grow out of, any usability impressions are irrelevant. This is also part of a bigger problem: the importance of in-context editing for sales has caused many CMS vendors to neglect their power user interface.
It is easy to understand why the sales demo gravitates to the in-context user interface: the audience finds it more intuitive. What is less obvious is why. In a typical CMS sales demonstration, the audience has the perspective of a site visitor. After all, this is not their site. They have no responsibility for it. As a site visitor, we think of editing the content that we see: "I see a typo;" "that sentence is hard to read;" "I would prefer to see another picture here." The user just wants to go in and fix it — like a Wikipedia article. Until it's fixed, that content issue is going to bug the user so directness and immediacy are critical. Like with a wiki, the in-context is ideal for solving these kinds of problems.
The content manager, however, has an entirely different perspective. The content manager is thinking more about the whole web site than any one page. The content manager has to solve problems like re-organizing the website and making global content changes. Needing to manually change every single page of a website is not acceptable so content reuse should be top of mind. From this perspective, the appearance of a page is less important than the actual content, which also includes information you can't see on the page but drives the behavior of the site. You can even go so far as to say that the visible page (what the visitor sees) actively hides information that the content manager needs to see. The visitor shouldn't know where else a piece of content is featured on the web site or what caused the personalization logic to show this item in this particular case — but the content manager does. Incidentally, this is why you should make product demos focus on scenarios. Scenarios force you to think about what the content manager does - not just dream of being able to edit somebody else's web site.
Yes, you can make the argument that the occasional content contributor (who 80% of the time experiences the site as a visitor) needs a simplified user interface to fix the issues that they notice or keep a few bits of information up to date. But, as an organization gets more sophisticated with managing content, those cases of simplistically managed pages (with no reuse and no presentation logic) get less frequent. At that point, you are just talking about the "about us" page and some simple press releases. Are you surprised that this is what your basic generic CMS demo shows? Furthermore, I am beginning to believe that the occasional user is a myth (another blog post).
In-context editing interfaces are steadily getting more powerful by exposing functionality like targeting and A/B testing but there inevitably comes a point when the content manager wants the full power of the application at his fingertips. As the in-context editors get better, that point gets pushed further out. But adding complexity and power to the in-context editing interface will no doubt steepen the learning curve for the occasional user and minimize the wow factor of the demo. And no CMS vendor will do anything to reduce the wow factor of their product demo.