Do web demos help people use interfaces?

Someone suggested to me recently that we should ship web demos with our products, as part of the user assistance offering. Since then, I've been trying to find evidence either for or against using web demos to help people understand interfaces, and I've come up with absolutely nothing.

There seem to be a couple of ways that web demos are used:

• to show a product to potential customers, particularly if the product is not yet available. Madcap Flare and AuthorIT are a couple I've recently watched.
• in an e-learning context

My gut reaction is that web demos are not likely to be particularly useful for providing interface and system assistance. We know that e-learning is a very different usability challenge from task-based interfaces (I saw this convincing presentation (pdf), by Florence Dujardin, on this subject at the Tekom conference last autumn), and while marketing people might think it's a great idea to ship marketing information with the product, users generally disagree.

We also know that users generally try and discover how things work by experimenting in the interface, and then resort to other sources of information when they get stuck. This implies we should (a) have more self-revealing interfaces, and (b) provide contextual assistance at the point of use.

When they do try and access assistance, they generally have very low tolerance for contextual information – they want to jump straight to their answer, and frequently scan text rather than reading it. This implies that we need to concentrate on providing and highlighting answers to common questions.

So how do web demos fit into this? It seems to me that people need to make a (relatively) big investment in learning about your interface to find them useful. Most people don't care about your interface – they care about getting this report done so they can go home, or getting the answer they need to impress their boss. Maybe in some marginal cases, they want to sit down and be guided through a demonstration/illustration of some complex tasks, but I'm not convinced it's a very compelling need.

What I would love is to find some real facts on this, rather than what I have now – mildly informed opinion. If anyone could point me in the right direction, I'd appreciate it.