I noticed that a lot of talks and presentations I attend, especially in the more academic circles, begin with the speaker showing a slide with the outline of the talk in form of a bulleted list and talks through it, explaining what he will talk about. With short talks this can actually take a significant part of the total time, especially if the speaker returns to that slide after each part, showing how far into the talk he progressed.
What is the point of that, short of giving the audience an opportunity for one last glance of their email client? The purpose of such an overview in printed articles is to give the reader some idea of the contents. This means that you can skip reading it altogether and move to the next article if the table of contents doesn't give you enough confidence that the article will be of use to you. Via page numbering it also allows you to skip directly to the interesting part, should only a part of the document be useful.
None of these uses apply to the spoken word though. You can't fast forward to the interesting bit and if you find that the talk won't be worth your time after the introduction it's usually considered quite rude to walk out at that point. As is browsing the web waiting for the part the interests you.
Some may argue that the table of contents makes the slide stack more readable in stand-alone form. I don't buy that - slides are part of the presentation and I don't think any consideration should be given on how useful they might be without the accompanying speech. It's 2012 after all and making at least an audio recording with cheap equipment shouldn't be science fiction anymore.